ICSE Class 10 Maths: GST Explained with Solved Examples

Ever wondered why the price on a candy bar jumps a bit after you add tax? That extra bit is usually GST, and it’s something you’ll see everywhere in commercial maths.

💡 In Simple Words: GST is a tax added to the price of goods or services. You first find the original price, work out a small percentage of it (the GST), and then add that amount to get the final price you pay.

Understanding GST in ICSE Commercial Mathematics

GST stands for Goods and Services Tax. Think of it as a single nationwide tax that replaces many smaller taxes. In everyday life it works like this: imagine water flowing through a pipe; the water is the money, and the pipe’s restriction (the GST rate) decides how much extra water (tax) is added.

Key terms you need to know

• Taxable value – the original price of the product before any tax.
• GST rate – the percentage the government says you must add (common rates are 5%, 12%, 18% and 28%).
• GST amount – the actual money you add, found by multiplying taxable value by GST rate.
• Gross price – the final price you pay after GST is added.

How to calculate GST – a simple 4‑step method

Let’s walk through each step with a real‑world example.

Example 1: Finding the GST amount and final price

Suppose a notebook costs ₹120 and the GST rate is 12%.

1. Taxable value = ₹120.
2. GST amount = 120 × 12/100 = ₹14.40.
3. Gross price = 120 + 14.40 = ₹134.40.

So you’d pay ₹134.40 for the notebook.

Example 2: Working backwards – given the gross price, find the original price

Imagine you bought a T‑shirt for ₹560 inclusive of 18% GST. What was its price before tax?

1. Let the taxable value be x. Then Gross price = x + 18% of x = x × (1 + 0.18) = 1.18x.
2. Set up the equation: 1.18x = 560.
3. Solve for x: x = 560 ÷ 1.18 ≈ ₹474.58.
4. GST amount = 560 – 474.58 ≈ ₹85.42.

The shirt’s original price was about ₹474.58, and the GST you paid was ₹85.42.

Example 3: Different GST rates for the same product

In some states, essential items attract a lower GST. Let’s compare a bottle of cooking oil priced at ₹200.

• In State A, GST = 5%: GST amount = 200 × 0.05 = ₹10, Gross price = ₹210.
• In State B, GST = 12%: GST amount = 200 × 0.12 = ₹24, Gross price = ₹224.

This shows why the same product can cost more in one region than another.

Quick Comparison Table

Common Mistakes to Avoid

• Mixing up the GST rate with the GST amount. The rate is a percent; the amount is money.
• Forgetting to convert the percent to a decimal (12% → 0.12) before multiplying.
• When working backwards, dividing by (1 + rate) instead of just the rate.
• Ignoring that GST is applied on the taxable value, not on the already‑taxed amount.

📝 Likely Exam Questions

1. A pair of shoes is sold for ₹2,500 inclusive of 18% GST. Find the price before GST and the GST amount.
   Answer: Let x be the taxable value. 1.18x = 2500 → x = 2500 ÷ 1.18 ≈ ₹2,118.64. GST = 2500 – 2118.64 ≈ ₹381.36.
2. Calculate the gross price of a mobile charger costing ₹350 before tax, if the GST rate is 28%.
   Answer: GST = 350 × 0.28 = ₹98. Gross price = 350 + 98 = ₹448.
3. If a laptop’s gross price is ₹45,000 and the GST rate is 12%, what is the taxable value?
   Answer: Taxable value = 45,000 ÷ 1.12 ≈ ₹40,178.57.
4. Two items are bought together: a book for ₹150 (5% GST) and a pen for ₹30 (12% GST). Find the total amount payable.
   Answer: Book GST = 150 × 0.05 = ₹7.50 → Book total = ₹157.50.
   Pen GST = 30 × 0.12 = ₹3.60 → Pen total = ₹33.60.
   Total = 157.50 + 33.60 = ₹191.10.
5. Explain why the same product may have different gross prices in two states, using GST rates.
   Answer: GST rates can vary by state for certain goods. A higher rate adds a larger tax amount, raising the final price, while a lower rate keeps the price closer to the original value.

Master these steps, and GST will feel as easy as adding two numbers on a calculator. Good luck with your ICSE Commercial Mathematics exam!