## Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole

# Chapter 12 - Section 12.2 - Arithmetic Sequences - 12.2 Exercises - Page 857: 70

#### Answer

$\displaystyle \frac{15}{4}$

#### Work Step by Step

The reciprocals of 3 and 5 are $\displaystyle \frac{1}{3}$ and $\displaystyle \frac{1}{5}$ Their average is $\displaystyle \frac{\frac{1}{3}+\frac{1}{5}}{2}=\frac{\frac{5+3}{15}}{\frac{2}{1}}=\frac{8\cdot 1}{15\cdot 2}=\frac{4}{15}$ The reciprocal of the average (the harmonic mean) is $\displaystyle \frac{15}{4}$

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