CA Foundation · Quantitative Aptitude · Ratio and Proportion, Indices and Logarithms
The ratio of boys to girls in a coaching class is 7 : 5. If 12 more girls join, the ratio becomes 7 : 8. How many boys are in the class?
There are 28 boys. Taking boys as 7k and girls as 5k, the new ratio gives 8 × 7k = 7(5k + 12), so 3k = 12 and k = 4. Boys are therefore 7 times 4, which is 28.
- A28
- B35
- C42Correct
- D49
Explanation
Let boys = 7k and girls = 5k. After joining, 7k/(5k+12) = 7/8, so 8k = 5k + 12 and k = 4. Boys = 7 × 4 = 28. Check: girls 20, then 32, and 28:32 = 7:8. So the answer is 28.
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