Question

your classmate is starting a new fitness program. He is planning to ride his bicycle 60 minutes every day. He burns 7 calories per minute bicycling at 11mph and 11.75 calories per minute bicycling at 15 mph. How long should he bicycle at each speed to burn 600 calories per hour?

Answer 1

Let the number of minutes he spent bicycling at 11mph be x and the number of minutes spent bicycling at 15mph be y, then

x + y = 60 . . . (1)
7x + 11.75y = 600 . . . (2)

(1) x 7 => 7x + 7y = 420 . . . (3)
(2) - (3) => 4.75y = 180
y = 180 / 4.75 ≈ 38 minutes

From (1), x + 38 = 60
x = 60 - 38 = 22 minutes

Therefore, he will spend 22 minutes bicycling at 11 mph and 38 minutes bicycling at 15 mph.