Question

Find the fourth proportional in $2.1,1.5,10.5$.

Answer 1

Explanation:

Let the fourth proportional be $\text{x}$.

Then, the numbers becomes in proportion.

$\text{⇒2.1:1.5::10.5:x}$

We know that ,$\text{Product of extremes = Product of means}$

$$\begin{gathered} \text{⇒x×2.1=1.5×10.5} \\ \text{⇒2.1x=15.75} \\ \text{⇒x=}\frac{15.75}{2.1} \\ \Rightarrow \mathrm{x}=7.5 \end{gathered}$$

Hence, the fourth proportional is $7.5$.