Final answer:
Mandy's target heart rate for exercise at 80% intensity is 160 beats per minute, calculated using the formula 220 minus her age (20 years), then multiplying the result by 0.80.
Step-by-step explanation:
Mandy, who is 20 years old, wants to calculate her target heart rate for exercise based on a target of 80 percent of her maximum heart rate. The formula for maximum heart rate is 220 minus the individual's age. Therefore, for Mandy, the maximal heart rate would be 220 - 20 = 200 beats per minute (bpm). To find her target heart rate for exercise at 80 percent, we multiply the maximum heart rate by 0.80 (80%). This results in a target heart rate of 200 bpm × 0.80 = 160 bpm.
The correct answer for Mandy's target heart rate for exercise is b. 160. This is the heart rate she should aim for during her workouts to meet her weight loss goals effectively.