Question 75

Find two numbers such that their mean proportional is 18 and the third proportional to them is 144.

Solution

$$\frac{x}{18}=\frac{18}{y}\ .$$

or, $$xy=18^2.$$...................(1)

Again,

$$\frac{x}{y}=\frac{y}{144}\ .$$

or, $$x=\frac{y^2}{144}\ .$$

So, from eq (1) :

$$\frac{18^2}{y}=\frac{y^2}{144}\ .$$

or, $$y^3=18^2\times144\ .$$

or, $$y=36.$$

So, $$x=\frac{18^2}{36}=9\ .$$

B is correct choice.

Share on Whatsapp Share on Whatsapp

Create a FREE account and get: