Why GST shows up on every receipt you get
Ever wonder why the price you see on a tag isn’t the amount you actually pay? That extra bit is GST – a tax that’s added to most goods and services in India. Knowing how to work it out is a must for ICSE Commercial Mathematics.
💡 In Simple Words: GST (Goods and Services Tax) is a single tax added to the price of things you buy. If something costs Rs 100 and the GST rate is 10%, you pay Rs 110. The extra Rs 10 is the tax.
GST Basics for a 10‑year‑old
GST rate is the percentage the government says you must add. Think of it like a recipe: if the recipe says add 5% sugar, you put in 5 grams for every 100 grams of flour. Here the “flour” is the original price, and the “sugar” is the tax.
Key terms
- Exclusive price: the cost before GST is added (the “flour”).
- Inclusive price: the total you actually pay, tax included (the “cake”).
- GST amount: the money that goes to the government, calculated as (rate/100) × exclusive price.
Step‑by‑step GST calculation
Let’s walk through the process like filling a water tank: first you know how much water (price) you start with, then you add a set amount (tax) and finally see the total level.
Example 1: Find GST amount and final price
Original (exclusive) price = Rs 1,200
GST rate = 18%
Step 1: GST amount = 1,200 × 18 ÷ 100 = Rs 216
Step 2: Inclusive price = 1,200 + 216 = Rs 1,416
So, you’d pay Rs 1,416 for an item that’s marked Rs 1,200 before tax.
Example 2: Given the inclusive price, recover the exclusive price
Inclusive price = Rs 2,360
GST rate = 12%
Step 1: Convert rate to a decimal factor: 12% = 0.12
Step 2: Inclusive price = exclusive × (1 + 0.12) → exclusive = 2,360 ÷ 1.12 = Rs 2,107.14 (rounded to 2 d.p.)
Step 3: GST amount = 2,360 – 2,107.14 = Rs 252.86
Thus the original price was about Rs 2,107.14 and the tax collected was Rs 252.86.
Quick comparison: Exclusive vs Inclusive
| Scenario | What you know | What you find |
|---|---|---|
| Exclusive price given | Original price & GST % | GST amount and inclusive price |
| Inclusive price given | Final price & GST % | Original price and GST amount |
Bullet summary
- GST is a percentage of the exclusive price.
- GST amount = (rate ÷ 100) × exclusive price.
- Inclusive price = exclusive price + GST amount.
- To reverse, exclusive price = inclusive ÷ (1 + rate/100).
📝 Likely Exam Questions
- Question: An article costs Rs 850 before GST. If the GST rate is 5%, calculate the GST amount and the price you pay.
Answer: GST = 850 × 5 ÷ 100 = Rs 42.5. Inclusive price = 850 + 42.5 = Rs 892.5. - Question: The inclusive price of a mobile phone is Rs 18,700 and the GST rate is 18%. Find the exclusive price and the GST amount.
Answer: Exclusive = 18,700 ÷ 1.18 = Rs 15,847.46 (≈). GST = 18,700 – 15,847.46 = Rs 2,852.54. - Question: A shop advertises “All items at 10% GST inclusive”. If a shirt’s displayed price is Rs 1,650, what is its price before GST?
Answer: Exclusive = 1,650 ÷ 1.10 = Rs 1,500. GST = 150. - Question: Compute the GST amount for a laptop priced at Rs 32,000 after a 12% GST is applied.
Answer: GST = 32,000 × 12 ÷ 112 = Rs 3,428.57 (using inclusive method) or find exclusive first: exclusive = 32,000 ÷ 1.12 = 28,571.43; GST = 32,000 – 28,571.43 = Rs 3,428.57.