Question

Medical researchers have determined that for exercise to be beneficial, a person’s desirable heart rate, R, in beats per minute, can be approximated by the formulas

for women
for men,

where a represents the person’s age. If the desirable heart rate for a man is 135 beats per minute, how old is he?

a.
22.5 years old
b.
40 years old
c.
45 years old
d.
42.5 years old


 

Please select the best answer from the choices provided

Answer 1

The functions that model R for men and women are missing.

Nevertheless, I searched for them and here they are:

For women, R = 143 - 0.65a

For men, R = 165 - 0.75a

You are asked for the age of a man whose desirable R is 135, so you must use the equation for men, R = 165 - 0.75a, replace 135 for R and solve for a.

=> 135 = 165 - 0.75a

=> 0.75 a = 165 - 135

=> 0.75 a = 30

=> a = 30 / 0.75

=> a = 40.

Answer: option b. 40 years old.