Question

Find the fourth proportion to 1.2, 1.6 and 7.2.

• A. 9.6
• B. 6.9
• C. 5.4
• D. 2.6

Answer 1

The correct option is

A

9.6

Let the fourth proportion be $x$.
Then, 1.2, 1.6, 7.2, $x$ are in proportion.

Product of means = Product of extremes
$\Rightarrow 1.6\times 7.2=x\times 1.2$
$\Rightarrow 1.2x=1.6\times 7.2$
$\Rightarrow x=\frac{1.6\times 7.2}{1.2}$
$\Rightarrow x=9.6$