## Introductory Algebra for College Students (7th Edition)

$a. \displaystyle \quad H=\frac{7}{8}(220-a)$ $b. \quad 175$ beats per minute.
$a.$ Based on the form of the formulas in previous exercises, we will subtract the age from 220, and multiply with the wanted factor of heart rate $H=\displaystyle \frac{7}{8}(220-a)$ $b.$ Substitute 20 for a $H=\displaystyle \frac{7}{8}(220-20)=\frac{7\cdot 200}{8}$ ... reduce the fraction with $8$ $= \displaystyle \frac{7\cdot 25}{1}$ $=175$ beats per minute.