When x is added to each of 9, 15, 21 and 31, the numbers so obtained are in proportion. What is the mean proportional between the numbers (3x -2) and (5x + 4)?
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 35
Concept
When numbers are in proportion, it can be written as a/b = c/d
Application
(9+x)/ (15+x) = (21+x)/(31+x)
Cross Multiplying, we get
x2 + 40x + 279 = x2 + 36x + 315
Upon solving
x = 9
We know that Mean Proportion of two numbers x and y = √xy
According to question, we need to find the mean proportion of (3x -2) and (5x + 4)
Putting the value of x, we get numbers - 25 and 49
Therefore, Mean Proportion = √25 x 49
= 5 x 7
= 35