Question

Find the fourth proportional to 1.4, 3.2 and 7.

Answer 1

Let the fourth proportional be $$x$$.

Then, $$\text{Product of extremes} = \text{Product of means}$$.

$$1.4 : 3.2 :: 7 : x$$

$$1.4 \times x = 3.2 \times 7$$

$$x = \frac{3.2 \times 7}{1.4} = \frac{22.4}{1.4} = 16$$