Question

Find fourth proportional to 6, 8 and 9?

Answer 1

Solution:

Let a be the required fourth proportional. 

Then 6:8 :: 9:a

or $\frac{6}{8}=\frac{9}{a}$

$⇒ 6a=8 \times 9$

$⇒ 6a=72$

$⇒ a=\frac{72}{6}=12$

Thus, the required fourth proportional is 12.

The required fourth proportional is 12.