Question

If 4, a, a, 36 are in proportion, then a =

(a) 24
(b) 12
(c) 3
(d) 24

Answer 1

(b) 12

4, a, a, 36 are in proportion; therefore, we get:

4 : a : : a : 36

$$\begin{gathered} \Rightarrow \frac{4}{a}=\frac{a}{36} \\ \Rightarrow 4\times 36=a\times a \\ \Rightarrow 144=a^2 \\ \Rightarrow a=12 \end{gathered}$$