Question

If 9, x, x and 49 are in proportion, find the value of x.

• A. 7
• B. 14
• C. 21
• D. 35

Answer 1

The correct option is C 21

Given: 9, x, x, 49 are in proportion i.e. 9:x :: x:49
$\Rightarrow \frac{9}{x}=\frac{x}{49}$
$\Rightarrow x\times x=9\times 49$
$\Rightarrow x\times x=441$
$\Rightarrow x\times x=21\times 21$
$\Rightarrow x=21$