Question

Find the fourth proportional to 9, 6, and 3.

Answer 1

Let the fourth proportional be x

So, we have 9 : 6 :: 3 : x

$\Rightarrow$ $\frac{9}{6}=\frac{3}{x}$

On cross-multiplication,
$\Rightarrow$ 9x = 18
$\Rightarrow$ x = 2

Hence, the fourth proportional to 9, 6 and 3 is 2.