One hour of bicycle riding can require 500-900 kcal of energy, depending on the speed, the terrain, and the weight of the racer. An individual wants to lose weight by riding at a modest effort, consuming 505 kcal of energy per hour. How many hours must he ride to lose 21.0 pounds of body fat? One gram of body fat is equivalent to 7.70 kcal of energy. There are 454 g in 1 lb.

Since one hour of riding a bicycle takes up 505 kcal of energy. It is also stated that one gram of body fat is equal to 7.70 kcal. Also, it is given that 1 pound of body fat is equal to 454 g.

Hence;

1 Ib= 454 g

21 Ib= 21 × 454/1 = 9534 g

But

1g of body fat = 7.70kcal

9534 g of body fat = 9534 × 7.70 kcal/1 = 73411.8 kcal

If 505 kcal is lost in 1 hour

73411.8 kcal is lost in 73411.8 kcal × 1hour/505k cal = 145 hours