Question

Your classmate is starting a new fitness program. He is planning to ride his bicycle 45 minutes every day. He burns 6 calories per minute bicycling at 11 mph and 9.75 calories per minute bicycling at 15 mph. How long should he bicycle at each speed to burn 300 ​calories?
He should bicycle for _ minutes at 11 mph and _ minutes at 15 mph.

Answer 1

Let x be the time at 11 mph, and let y be the time at 15 mph.
x + y = 45 ............(1)
Therefore:
y = 45 - x ............(2)

Now we can write the equation for the total calories required:
6x + 9.75y = 300 ........(3)

Plugging the value for y from equation (2) into equation (3), we get:
6x + 9,75(45 - x) = 300 .......(4)
which simplifies to:
-3.75x = -138.75
x = -138.75/-3.75 = 37 minutes.
The answer is 37 minutes at 11 mph and 8 minutes at 15 mph.