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In a Coimbatore school, 12% of the 500 junior-section students and 20% of the 300 senior-section students joined the science club. What percent of the whole school joined?

Class 8Comparing QuantitiesComparing Quantities
  • A15%
  • B16%
  • C32%
  • D24%

Step-by-Step Solution

Juniors: 12% of 500 = 60. Seniors: 20% of 300 = 60. Together 120 club members out of 500 + 300 = 800 students, so %. Trap: averaging the two rates gives 16% and adding them gives 32% — neither allows for the sections being different sizes; 24% divides by the junior total alone.
Answer: A) 15%

Key idea: Discount

A discount is a reduction off the **marked price** (MP), not the cost price. The selling price (SP) is what the customer actually pays.

**SP = MP − Discount**
**Discount % = (Discount / MP) × 100**

Example: shirt MP ₹800, discount 25%. Discount amount = 25% of 800 = 200. SP = 800 − 200 = 600.

Note: discount % is calculated on MP. Profit/loss % (Class 7) is on CP. Don't mix them up.

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