The mean proportional between 36 and a number N is three times the mean proportional between 8 and 32. The number N is:
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 64.
Mean proportional between 8 and 32 = √(8 × 32) = √256 = 16
Three times this = 3 × 16 = 48
Let N be the number. Mean proportional between 36 and N = √(36 × N) = 48
⇒ 36 × N = 48 × 48 = 2304
⇒ N = 2304 ÷ 36 = 64