To solve this problem you must apply the proccedure shown below:
 1- Let's give values to the weight of each fruit:
 orange=0.5 kg
 grapefruit=(0.5)+(0.08)(0.5 kg)=0.54 kg
 apple=(0.5)-(0.1)(0.5 kg)=0.45 kg
 2- Therefore, you have:
 %=100%-(apple/grapefruit)x100
 %=100%-(0.45/0.54)X100
 %=16.66%
 The answer is: 16.66%