Multiple choice

The average age of a class was 15 years, when 5 boys whose average age was 12 years 6 months were admitted average of the class was reduced by 6 months. How many boys were there ? एक कक्षा की औसत आयु 15 वर्ष थी, जब 5 लड़के जिनकी औसत आयु 12 वर्ष 6 माह थी, शामिल किये जाते हैं, कक्षा का औसत 6 माह घट जाता है। वहां कक्षा में कितने लड़के थे?

  1. 20

  2. 170

  3. 270

  4. 200

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let original boys = n, total age = 15n. New total age = 15n + 5(12.5) = 15n + 62.5. New average = (15n + 62.5)/(n + 5) = 14.5. Solving: 15n + 62.5 = 14.5n + 72.5, so 0.5n = 10, n = 20.