Question

Find fourth proportional to each of the following:

(ii)$1.5,4.5,3.5$

Answer 1

Find the fourth proportional:

If $y$ is the fourth proportional to the numbers $a,b,c$ then $a:b::c:y$.

Let $x$ be the required fourth proportional.

Hence, for the given numbers, $1.5:4.5::3.5:x$.

$$\begin{gathered} \Rightarrow 1.5:4.5=3.5:x(Changingtheproportionalitysigntoequalsign) \\ \Rightarrow \frac{1.5}{4.5}=\frac{3.5}{x} \\ \Rightarrow 1.5·x=4.5·3.5(Crossmultiplyingbothsides) \\ \Rightarrow x=\frac{4.5·3.5}{1.5}(Dividingbothsidesby1.5) \\ \Rightarrow x=3·3.5 \\ \therefore x=10.5 \end{gathered}$$

Final Answer: Therefore, the fourth proportional is $10.5$.