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GATE 2021 BT – Question 1

General Aptitude · Quantitative Aptitude: Arithmetic and Number Computation · 1 mark · Multiple choice

The ratio of boys to girls in a class is 7 to 3. Among the options below, an acceptable value for the total number of students in the class is:

  1. 21
  2. 37
  3. 50
  4. 73

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Show answer and explanation

Correct answer: (C) 50

Explanation

The ratio of boys to girls is $7:3$, so the number of boys is $7k$ and the number of girls is $3k$ for some positive whole number $k$ (the numbers of students must be whole numbers).

**Total:**
$$7k+3k=10k .$$

So the total must be a **multiple of 10**. Checking the options:
- 21, 37 and 73 are not multiples of 10. ✗
- **50** $=10\times5$ ($k=5$: 35 boys and 15 girls). ✓

Answer **50** (C).