Question

Find the fourth proportional of: ​(iii) $2.1,1.5$ and $8.4$.​

Answer 1

Let the fourth proportional be $x$.
$\therefore$ $2.1:1.5=8.4:x$
[$\because$ Ratio of first two terms $=$ Ratio of last two terms]
$\Rightarrow$ $\frac{2.1}{1.5}=\frac{8.4}{x}$
$\Rightarrow$ $x=\frac{1.5\times 8.4}{2.1}=6$
Hence, the fourth proportion is $6$.