Question

Find the fourth proportional to 1.5, 4.5 and 3.6.

Answer 1

Let the fourth proportional be $$x$$.

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

$$1.5 : 4.5 :: 3.6 : x$$

$$1.5 \times x = 4.5 \times 3.6$$

$$x = \frac{4.5 \times 3.6}{1.5} = 3 \times 3.6 = 10.8$$