The mean proportional between 25 and a number N is two times the mean proportional between 15 and 35. The number N is:
Show answer & explanation
Correct answer: D
Explanation
The correct answer is Option 4 i.e. 84.
Mean proportional between two numbers a and b = √(a × b)
Mean proportional between 25 and N = √(25 × N)
Mean proportional between 15 and 35 = √(15 × 35) = √525
Given: √(25 × N) = 2 × √525
⇒ √(25 × N) = 2 × √525
⇒ 25 × N = (2 × √525)2 = 4 × 525 = 2100
⇒ N = 2100 ÷ 25 = 84