If third proportional of 36 and 18 be x, then what is the value of x?

Correct option is D

Given:

First number = 36
Second number = 18
Third proportional = x

Formula Used:

If a, b, and x are in continued proportion, then b is the mean proportional between a and x. The formula for the third proportional is:

​$$\frac{a}{b} = \frac{b}{x}\implies x = \frac{b^2}{a}$$​​

Solution:

Substituting the given values:

​$$x = \frac{18^2}{36}$$​​

​$$x = \frac{324}{36}$$​​

x = 9