Percentages are a good way to describe fractions of quantities. They are used in everyday life to convey information as varied as amounts of fat in food and how much we can expect to save in a sale. Sanjeev Kohli goes to the gym to show that 100% is the maximum effort anyone can give. We hear from his instructor, Riccardo Scala, that percentages are vital to fitness training and nutrition. Sanjeev calculates percentages on the hop while training for the Celebrity Space Hopper Mathletes competition.