###### Example2.1.6Target heart rate

According to the American Heart Association, a person's maximum heart rate, in beats per minute (bpm), is given by $$220 - a\text{,}$$ where $$a$$ is their age in years.

1. Determine the maximum heart rate for someone who is $$31$$ years old.

2. A person's target heart rate for moderate exercise is $$50\%$$ to $$70\%$$ of their maximum heart rate. If they want to reach $$65\%$$ of their maximum heart rate during moderate exercise, we'd use the expression $$0.65(220-a)\text{,}$$ where $$a$$ is their age in years. Determine the target heart rate at this $$65\%$$ level for someone who is $$31$$ years old.

Explanation
in-context