Chapter 8, Problem 3RP

To determine

To find the mean proportional between 5 and 20.

Answer to Problem 3RP

The mean proportional between 5 and 20 is ±10.

Explanation of Solution

Given information:

First and fourth numbers are 5 and 20 respectively.

Formula used:

In a mean proportion, the means are the same.

Proportion is $\frac{a}{x}=\frac{x}{r}$

Calculation:

  $\begin{array}{l}\frac{a}{x}=\frac{x}{r}\\ \therefore \frac{5}{x}=\frac{x}{20}\\ \therefore x^2=100\\ \therefore x=\sqrt{100}\\ \therefore x=\pm 10\end{array}$