Question

Find the fourth proportion of 2 , 4 and 8

• A. 42
• B. 64
• C. 4
• D. 16

Answer 1

The correct option is D

16

Let the fourth proportion be $x$

$\Rightarrow$ 2 , 4 , 8 , $x$ are in proportion

$\therefore$ 2 : 4 = 8 : $x$

$\therefore$ $2\times x=4\times 8(\because \text{Product of extremes = Product of means})$

$\therefore$ $2x=32$

$x=16$

Hence the fourth proportion is 16.