Question

Find the value of $x$ so that the given four numbers are in proportion.

$7,x,21and45$

Answer 1

We know that if four numbers $a,b,candd$are in proportion.

then $a\times d=b\times c$ …………………………….$eq\left(1\right)$

so, here in $7,x,21and45$

$a=7,b=x,c=21,d=45$

the by $eq\left(1\right)$ we have,

$$\begin{gathered} \Rightarrow 7\times 45=x\times 21 \\ \Rightarrow 315=21x \\ \Rightarrow x=\frac{315}{21} \\ \Rightarrow x=15 \end{gathered}$$

Hence the value of $x=15$ for which the given four numbers $7,x,21and45$ are in proportions.