Question

Find out the fourth proportional to 4, 9, 12.

Answer 1

Let the fourth proportional to 4, 9, 12 be $x$
Then, $4:9::12:x$

$\Rightarrow 4\times x=9\times 12$

$\Rightarrow x=\frac{9\times 12}{4}=27$
$\therefore$ Fourth proportional to 4, 9, 12 is 27.