Question

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

$21,9,49andx$

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 $21,9,49andx$

$a=21,b=9,c=49,d=x$

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

$$\begin{gathered} \Rightarrow 21\times x=9\times 49 \\ \Rightarrow 21x=441 \\ \Rightarrow x=\frac{441}{21} \\ \Rightarrow x=21 \end{gathered}$$

Hence the value of $x=21$ for which the given four numbers $21,9,49andx$ are in proportions.