Question

Playing tennis burns energy at a rate of about 25 kJ/min. Cycling burns energy at about 35kJ/min. Hans exercised by playing tennis and then cycling. He exercised for 50 min altogether and used a total of 1450kJ of energy. For how long did he play tennis?

Answer 1

To answer this, you need to make a systems of equations.

25x + 35y = 1450
x + y = 50 ----> y = 50 - x

25x + 35(50-x) = 1450
25x + 1750 - 35x = 1450
25x - 35x + 1750 = 1450
-10x + 1750 = 1450
- 1750 -1750

-10x = -300
x = 30


He played tennis for 30min