Goods and Services Tax (GST) ICSE Class 10: Concepts, Formulas and Solved Questions

What Goods and Services Tax (GST) is about

Weightage: CISCE publishes no chapter or unit weightage for ICSE Mathematics. Goods and Services Tax (GST) is in the 1. Commercial Mathematics (i) Goods and Services Tax (GST) part of the 2027 syllabus and can be asked in both Section A and Section B of the 80-mark paper.Source: CISCE ICSE Mathematics syllabus, examination year 2027

Key concepts

What GST is charged on: the taxable value

GST is a tax on the supply (sale) of goods and services. The seller collects it from the buyer and pays it to the government.

The tax is worked out on the taxable value, which is the actual selling price of the article:

• If there is no discount, the taxable value is the marked price (list price).
• If there is a discount, take the discount off first. The taxable value is the price after discount.

So the order of work never changes: marked price → subtract discount → taxable value → add GST. GST is never charged on the marked price when a discount is given. The rate $r\%$ is given in the question; the tax is $\frac{r}{100}$ of the taxable value.

Worked example

An article is sold for ₹850 with no discount. The GST rate is 12%. Find the GST and the amount the buyer pays.

Try it first, then show the solutionSolution

1. No discount, so taxable value $=₹850$.
2. GST $=\frac{12}{100}\times 850=₹102$.
3. Amount paid $=850+102=₹952$.

Answer: GST = ₹102; the buyer pays ₹952.

Intra-state sale: CGST and SGST

When the seller and the buyer are in the same state, the sale is intra-state. The GST is split into two equal halves:

• CGST (Central GST), which goes to the Central government;
• SGST (State GST), which goes to the state government.

If the GST rate is $r\%$, then CGST is charged at $\frac{r}{2}\%$ and SGST at $\frac{r}{2}\%$. So CGST = SGST = half the GST.

Read every word of the question. 'The rate of GST is 18%' means CGST 9% + SGST 9%. 'CGST is charged at 9%' means the GST rate is 18%. If a question gives you the CGST amount, double it to get the GST amount before you do anything else.

Worked example

A shopkeeper in Lucknow sells a fan to a customer in Lucknow for ₹3,600. The GST rate is 18%. Find the CGST, the SGST and the total amount paid.

Try it first, then show the solutionSolution

1. Same state, so it is intra-state: CGST rate $=9\%$, SGST rate $=9\%$.
2. CGST $=\frac{9}{100}\times 3600=₹324$; SGST $=₹324$.
3. Total amount $=3600+324+324=₹4,248$.

Answer: CGST = SGST = ₹324; total = ₹4,248.

Inter-state sale: IGST

When the seller and the buyer are in different states, the sale is inter-state. The whole tax is collected as IGST (Integrated GST) at the full GST rate. There is no splitting into CGST and SGST in the bill.

The amount the buyer pays is the same either way: the taxable value plus $r\%$ of it. Only the name of the tax, and who collects it, changes. So in a question about an inter-state sale, never halve the rate.

Worked example

A trader in Surat (Gujarat) sells sarees worth ₹6,200 to a shop in Indore (Madhya Pradesh). The GST rate is 12%. Find the IGST and the bill amount. What would the CGST have been if the shop were also in Surat?

Try it first, then show the solutionSolution

1. Different states, so the whole tax is IGST at 12%.
2. IGST $=\frac{12}{100}\times 6200=₹744$; bill $=6200+744=₹6,944$.
3. If the sale were within Gujarat, CGST $=6\%$ of $6200=₹372$ (and SGST also ₹372).

Answer: IGST = ₹744; bill = ₹6,944. CGST would have been ₹372.

Discount first, then GST

Discount is always given on the marked price, and GST is charged on the price after the discount.

$\text{Taxable value}=\text{MP}-\text{discount}=\text{MP}\times \left(1-\frac{d}{100}\right)$
$\text{Amount paid}=\text{taxable value}\times \left(1+\frac{r}{100}\right)$

A common shortcut is to multiply by both factors in one line, for example $2400\times 0.85\times 1.05$. That is fine, but write the taxable value on its own line too, because the examiner gives a mark for it.

Worked example

The marked price of a school bag is ₹2,400. The shop gives a 15% discount and the GST rate is 5%. Find the amount the customer pays.

Try it first, then show the solutionSolution

1. Discount $=15\%$ of $2400=₹360$, so taxable value $=2400-360=₹2,040$.
2. GST $=5\%$ of $2040=₹102$.
3. Amount paid $=2040+102=₹2,142$.

Answer: ₹2,142

Inverse cases: working back from the amount paid

In an inverse question you are told the amount paid including GST and asked for the price before tax, the marked price, the discount or the rate.

If $A$ is the amount paid and the GST rate is $r\%$, then $A=V\left(1+\frac{r}{100}\right)$, so
$V=\frac{100\times A}{100+r}.$

Do not take $r\%$ of the amount paid and subtract it: the tax was charged on $V$, not on $A$. For example, if ₹1,180 includes 18% GST, the tax is ₹180, not 18% of 1,180 = ₹212.40.

To find the rate: GST amount = amount paid − taxable value, and rate $=\frac{\text{GST}}{\text{taxable value}}\times 100$.

Worked example

A customer pays ₹7,080 for a printer, including GST at 18%. Find the price of the printer before GST.

Try it first, then show the solutionSolution

1. Let the taxable value be ₹$V$. Then $V\times \frac{118}{100}=7080$.
2. $V=\frac{7080\times 100}{118}=₹6,000$.
3. Check: $18\%$ of $6000=1080$ and $6000+1080=7080$.

Answer: ₹6,000

Finding the rate of GST

When the taxable value and the tax (or the amount paid) are known, the rate is a simple percentage:
$r=\frac{\text{GST}}{\text{taxable value}}\times 100.$

If only the CGST (or SGST) amount is given, double it first. If a discount is involved, find the taxable value after the discount before you divide. The answer is a percentage, so write the % sign.

Worked example

On an article with taxable value ₹2,750, the SGST charged is ₹165. Find the rate of GST.

Try it first, then show the solutionSolution

1. GST $=2\times 165=₹330$ (CGST equals SGST).
2. Rate $=\frac{330}{2750}\times 100=12\%$.

Answer: 12%

Bills with several items and different rates

A bill question lists items with a price per unit, a quantity and a GST rate for each item. Work item by item:
1. Cost of the item = price per unit × quantity.
2. Take off any discount that applies (read the condition: for example 'on 10 or more articles').
3. GST on that item = its rate × its taxable value.
4. Add the GST of all items for the total GST, and add the taxable values and the GST for the bill amount.
5. Round only at the very end, and only if the question asks (for example, to the nearest ₹10).

A table with columns Item, Taxable value, Rate, GST keeps the working neat and is easy for the examiner to mark.

Worked example

A bill shows 2 kg of dry fruit at ₹240 per kg (GST 5%) and 6 notebooks at ₹85 each (GST 12%). Find the total GST.

Try it first, then show the solutionSolution

1. Dry fruit: $2\times 240=₹480$; GST $=5\%$ of $480=₹24$.
2. Notebooks: $6\times 85=₹510$; GST $=12\%$ of $510=₹61.20$.
3. Total GST $=24+61.20=₹85.20$.

Answer: ₹85.20

GST along a chain of sales (tax paid by each dealer)

Goods often pass from a manufacturer to a wholesaler to a retailer to the consumer. Each seller charges GST on their own selling price (output tax) and has already paid GST when buying (input tax). The seller pays the government only the difference:
$\text{GST payable by a dealer}=\text{output GST}-\text{input GST}.$

When the rate is the same at every stage, this equals the rate times the dealer's profit (selling price − cost price). Adding the tax paid at every stage gives exactly the GST on the final selling price, which is the tax the consumer pays. In an intra-state chain, each dealer's payment is split equally into CGST and SGST.

Worked example

In Jaipur, a manufacturer sells a sofa to a dealer for ₹12,000; the dealer sells it to a retailer for ₹15,000; the retailer sells it to a customer for ₹16,500. The GST rate is 5% throughout. Find the GST paid to the government at each stage.

Try it first, then show the solutionSolution

1. Manufacturer: $5\%$ of $12000=₹600$.
2. Dealer: $5\%$ of $15000-5\%$ of $12000=750-600=₹150$.
3. Retailer: $5\%$ of $16500-5\%$ of $15000=825-750=₹75$.
4. Check: $600+150+75=825=5\%$ of $16500$, the tax the customer pays.

Answer: ₹600, ₹150 and ₹75 at the three stages (₹825 in all).

Maths in real life: Goods and Services Tax (GST)

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Topics in this chapter

• CGST and SGST in an Intra-state Sale
• GST with Discount
• Inverse GST Problems

Goods and Services Tax (GST) formula sheet

Taxable value

$V=\text{MP}-\text{discount}=\text{MP}\left(1-\frac{d}{100}\right)$

GST is charged on V, never on the marked price when there is a discount.

GST on an article

$\text{GST}=\frac{r}{100}\times V$

The rate r% is always given in the question.

Intra-state split

$\text{CGST}=\text{SGST}=\frac{1}{2}\text{GST}$

Each is charged at half the GST rate.

Inter-state sale

$\text{IGST}=\frac{r}{100}\times V$

The full rate, not split.

Amount paid by the buyer

$A=V\left(1+\frac{r}{100}\right)$

Taxable value plus GST.

Inverse: price before GST

$V=\frac{100A}{100+r}$

Use when the amount paid includes GST.

Rate of GST

$r=\frac{\text{GST}}{V}\times 100$

Double the CGST or SGST first if only one is given.

Discount percent

$d=\frac{\text{MP}-V}{\text{MP}}\times 100$

Discount percent is always on the marked price.

Tax payable by a dealer in a chain

$\text{output GST}-\text{input GST}$

Same rate throughout: rate × (selling price − cost price).

How the board asks Goods and Services Tax (GST)

The question patterns to expect, and the method that works for each.

Tricks to remember Goods and Services Tax (GST)

Short memory aids. Say each one aloud once, then use it on a question the same day.

• D before T

  Discount before Tax, just as D comes before T in the alphabet.

  Use it when: Every problem with both a discount and GST.

• Same state, split the plate

  Intra-state: the GST plate is split into two equal halves, CGST and SGST. Inter-state: one whole plate, IGST.

  Use it when: Deciding whether to halve the rate.

• Divide by 1.r, don't subtract r%

  If the price includes 18% GST, divide by 1.18. If it includes 5%, divide by 1.05.

  Use it when: Inverse questions, so you never take the tax as a percentage of the amount paid.

• Double the half

  Given CGST or SGST? Double it before anything else to get the GST.

  Use it when: MCQs like 'CGST paid is ₹120, find the rate'.

• Chain tax = rate × value added

  Each dealer pays tax only on what they add: rate × (selling price − buying price).

  Use it when: Supply-chain questions with one rate throughout.

Goods and Services Tax (GST): board-level solved questions

Ordered from board level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section B style)

Read the situation, then answer every part. In the board paper this is a 10-mark question split into 3 + 3 + 4 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Goods and Services Tax (GST)

The slips examiners see most often, and what to write instead.

• ✗Mistake: Treating CGST as the whole GST

  CISCE examiners' comments, 2024: candidates did not realise that CGST is half of the total GST, so they took the given CGST of ₹120 as the whole GST and picked the wrong option.

  Wrong working

  CGST paid is ₹120 on ₹2,000, so the rate is $\frac{120}{2000}\times 100=6\%$.

  Right working

  GST $=2\times 120=₹240$, so the rate is $\frac{240}{2000}\times 100=12\%$.

  ✓Do this: Underline the word CGST, SGST or GST in the question. If it says CGST or SGST, double it first.

  Usually costs: The whole mark in an MCQ; in a long answer, every step after it.

• ✗Mistake: Using the CGST rate as the GST rate

  CISCE examiners' comments, 2025: when told 'CGST is charged at 4%', many took 4% as the full tax and added only that, or found only the CGST and stopped.

  Wrong working

  Price with GST $=1375+4\%$ of $1375=₹1,430$.

  Right working

  GST rate $=2\times 4\%=8\%$; price $=1375\times 1.08=₹1,485$.

  ✓Do this: Turn every CGST or SGST rate into the GST rate before you calculate, and add both CGST and SGST to the price.

  Usually costs: 1 mark in Section A.

• ✗Mistake: Charging GST on the price of one unit

  CISCE examiners' comments, 2024: in a bill question, candidates worked out the tax on the price per kg or per piece instead of on the cost of the whole quantity.

  Wrong working

  Laddoos at ₹500 per kg, 2 kg, GST 5%: GST $=5\%$ of $500=₹25$.

  Right working

  Cost $=2\times 500=₹1,000$; GST $=5\%$ of $1000=₹50$.

  ✓Do this: Make a 'cost = price × quantity' column in your table before the GST column.

  Usually costs: 1 to 2 marks in a 3-mark bill question.

• ✗Mistake: Stopping before the total asked for

  CISCE examiners' comments, 2024: candidates found the GST of each item but not the total GST, or did not add the tax to get the bill amount.

  ✓Do this: Before you start, write down what the last line must be ('Total bill = ...'). Tick each part of the question as you answer it.

  Usually costs: 1 mark for each missing final step.

• ✗Mistake: Missing a discount condition or the rounding instruction

  CISCE examiners' comments, 2025: in a bill with a note like 'discount on 10 or more articles', candidates missed the condition, and did not round the total to the nearest ₹10 as asked.

  ✓Do this: Read the notes under a bill twice. Write 'discount applies' or 'does not apply' next to each item, and round only in the last line.

  Usually costs: Up to 2 marks of a 4-mark part.

• ✗Mistake: Taking the tax as a percentage of the amount paid

  In inverse questions the amount paid already includes GST, but students subtract r% of it.

  Wrong working

  ₹4,130 includes 18% GST, so price $=4130-18\%$ of $4130=₹3,386.60$.

  Right working

  Price $=\frac{4130\times 100}{118}=₹3,500$.

  ✓Do this: Write the equation $V(1+\frac{r}{100})=A$ and solve it for $V$.

  Usually costs: Most of a 4-mark inverse question.

• ✗Mistake: Not giving money to two decimal places

  CISCE examiners' comments, 2024 (suggestions for candidates): answers in rupees should be given correct to two decimal places when they are not whole numbers.

  ✓Do this: Write ₹489.60, not ₹489.6 or ₹490, unless the question asks you to round.

  Usually costs: The accuracy mark in the final line.

Practice questions on Goods and Services Tax (GST)

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQBoard level

   A trader in Delhi sells an article to a buyer in Haryana for ₹2,500. The rate of GST is 18%. The IGST charged is:
   (a) ₹225
   (b) ₹450
   (c) ₹2,950
   (d) ₹900

   Hint

   Different states: the whole tax is IGST.

   Answer

   (b) ₹450, since $18\%$ of $2500=450$.

2. Q2 · 1 mark · MCQBoard level

   An article costs ₹1,180 including GST at 18%. The GST paid is:
   (a) ₹212.40
   (b) ₹180
   (c) ₹118
   (d) ₹90

   Hint

   Find the price before tax first.

   Answer

   (b) ₹180. Price before GST $=\frac{1180}{1.18}=1000$, so GST $=180$.

3. Q3 · 1 mark · MCQHarder board level

   In an intra-state sale, the SGST charged on an article is ₹54 and the rate of GST is 12%. The amount paid by the customer is:
   (a) ₹954
   (b) ₹1,008
   (c) ₹1,062
   (d) ₹1,116

   Hint

   Double the SGST, then find the taxable value.

   Answer

   (b) ₹1,008. GST $=108$, taxable value $=\frac{108\times 100}{12}=900$, amount $=900+108=1008$.

4. Q4 · 1 mark · Assertion-reasonBoard level

   Assertion (A): For an article with taxable value ₹1,000, the amount paid rises by ₹60 when the GST rate is raised from 12% to 18%.
   Reason (R): The change in the tax equals the change in the rate applied to the taxable value.
   (a) (A) is true and (R) is false.
   (b) (A) is false and (R) is true.
   (c) Both (A) and (R) are true, and (R) is the correct explanation for (A).
   (d) Both (A) and (R) are true, but (R) is not the correct explanation for (A).

   Hint

   Find 6% of 1,000.

   Answer

   (c). The change is $6\%$ of $1000=₹60$, which is exactly what (R) describes.

5. Q5 · 4 marks · Short answerHarder board level

   The marked price of an air cooler is ₹8,500. A discount of 12% is given and GST is charged at 28% in an intra-state sale. Find (a) the CGST, (b) the amount paid by the customer.

   Hint

   Taxable value first; CGST rate is 14%.

   Answer

   Taxable value $=8500\times 0.88=₹7,480$.
   (a) CGST $=14\%$ of $7480=₹1,047.20$.
   (b) Amount $=7480\times 1.28=₹9,574.40$.

6. Q6 · 4 marks · Short answerHarder board level

   After a flat discount of ₹500, a customer pays ₹5,310 for a bicycle, including GST at 18%. Find the marked price of the bicycle.

   Hint

   Work back from ₹5,310 to the price after discount, then add the discount back.

   Answer

   Price after discount $=\frac{5310\times 100}{118}=₹4,500$; marked price $=4500+500=₹5,000$.

7. Q7 · 4 marks · Short answerHarder board level

   An article marked at ₹2,400 is sold at a discount of 10%. The customer pays ₹2,268 including GST. Find the rate of GST.

   Hint

   Taxable value, then tax = amount paid − taxable value.

   Answer

   Taxable value $=2400\times 0.9=₹2,160$; GST $=2268-2160=₹108$; rate $=\frac{108}{2160}\times 100=5\%$.

8. Q8 · 3 marks · Long answerBoard level

   A shopkeeper buys a mixer for ₹3,000 and marks it 40% above the cost price. He sells it at a discount of 10%, and GST is charged at 12%. Find (a) the amount paid by the customer, (b) the shopkeeper's profit percent (ignore the GST, which he passes on to the government).

   Hint

   Marked price = 1.4 × cost; selling price = 0.9 × marked price.

   Answer

   Marked price $=3000\times 1.4=₹4,200$; selling price $=4200\times 0.9=₹3,780$.
   (a) Amount paid $=3780\times 1.12=₹4,233.60$.
   (b) Profit $=3780-3000=₹780$; profit percent $=\frac{780}{3000}\times 100=26\%$.

9. Q9 · 4 marks · Long answerHarder board level

   A dealer sells an article at a profit of 25% on his cost. The customer pays ₹5,900, including GST at 18%. Find the dealer's cost price.

   Hint

   Two inverse steps: remove the GST, then remove the profit.

   Answer

   Selling price before GST $=\frac{5900}{1.18}=₹5,000$. Cost price $=\frac{5000}{1.25}=₹4,000$.

10. Q10 · 4 marks · Long answerHarder board level

    A wholesaler in Chennai buys goods for ₹15,000 and sells them to a retailer in Chennai for ₹18,000. The retailer sells them to a consumer in Chennai for ₹21,000. The GST rate is 18%. Find (a) the CGST and SGST paid by the retailer to the government, (b) the amount paid by the consumer.

    Hint

    Retailer pays output GST − input GST.

    Answer

    (a) Output GST $=18\%$ of $21000=₹3,780$; input GST $=18\%$ of $18000=₹3,240$; payable $=₹540$, so CGST $=₹270$ and SGST $=₹270$.
    (b) Consumer pays $21000\times 1.18=₹24,780$.

11. Q11 · 4 marks · Long answerHOTS / competency

    When the GST rate on an article is cut from 18% to 5%, the amount a customer pays falls by ₹390. Find (a) the taxable value of the article, (b) the amount paid before and after the cut.

    Hint

    The fall equals 13% of the taxable value.

    Answer

    (a) $13\%$ of $V=390$, so $V=\frac{390\times 100}{13}=₹3,000$.
    (b) Before: $3000\times 1.18=₹3,540$; after: $3000\times 1.05=₹3,150$. Check: $3540-3150=390$.

12. Q12 · 3 marks · Short answerHOTS / competency

    A shopkeeper wants a customer to pay exactly the marked price of an article, including GST at 18%. Show that he must give a discount of $\frac{18}{118}\times 100\%$, and write this correct to two decimal places. Does the answer depend on the marked price?

    Hint

    Let the marked price be M and solve $1.18V=M$.

    Answer

    $1.18V=M$ gives $V=\frac{M}{1.18}$. Discount $=M-\frac{M}{1.18}=\frac{0.18M}{1.18}$, so discount percent $=\frac{18}{118}\times 100=15.25\%$ (to 2 d.p.). The M cancels, so the answer does not depend on the marked price, only on the rate.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.On what amount is GST charged when a discount is given?Show answer

   On the price after the discount (the taxable value).

2. 2.In an intra-state sale at 18% GST, what are the CGST and SGST rates?Show answer

   9% each.

3. 3.What tax is charged in an inter-state sale, and at what rate?Show answer

   IGST, at the full GST rate.

4. 4.A price of ₹A includes GST at r%. Write the price before tax.Show answer

   $\frac{100A}{100+r}$

5. 5.The SGST on an article is ₹30. What is the total GST?Show answer

   ₹60, since CGST equals SGST.

6. 6.How much GST does a dealer pay to the government in a chain of sales?Show answer

   Output GST minus input GST.

7. 7.Does the buyer pay more in an inter-state sale than an intra-state one at the same rate?Show answer

   No. The total tax is the same; only its name (IGST or CGST + SGST) changes.

8. 8.Is the discount percent worked on the marked price or the price paid?Show answer

   On the marked price.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you find the taxable value after a discount and charge GST on it?
• ☐Can you split GST into CGST and SGST, and recognise when the sale is inter-state (IGST)?
• ☐Given only the CGST amount and the rate, can you find the price?
• ☐Can you work back from an amount including GST to the price before tax and to the marked price?
• ☐Can you find the discount percent needed so that a customer pays a fixed amount?
• ☐Can you set out a bill with several items and rates in a table, and round only at the end?
• ☐Can you find the tax paid by one dealer in a chain of intra-state sales?

Goods and Services Tax (GST): frequently asked questions