Question

Regular exercise can help a person lower their resting heart rate. Suppose an individual’s resting heart rate, in beats per minute, is modeled by the function f(x) = –0.1x 3 + 0.6x 2 + 85 after x weeks of regular exercise.

How many weeks of exercise are necessary to lower the individual’s resting heart rate below 70 beats per minute?

7 weeks
8 weeks
9 weeks
10 weeks

Answer 1

9

Explanation:

Answer 2

Answer: 9 weeks

Explanation:

-0.1³ + 0.6x² + 85 = 70

x ≈ 8.21998224

The answer is 9 weeks because you must round 8.22 up to 9. The reason you round up to 9 is because must include the numbers after the decimal in a week, but you cannot have 0.22 weeks, so 0.22 rounds up to 1.