Question

Find the fourth proportional of : ​$3,12$ and $4$.​

Answer 1

Let the fourth proportional be $x$.
$\therefore$ $3:12=4:x$
[$\because$ Ratio of first two terms $=$ Ratio of last two terms ]
$\Rightarrow$ $\frac{3}{12}=\frac{4}{x}$
$\Rightarrow$$x=\frac{4\times 12}{3}=16$
Hence, the fourth proportion is $16$.