To solve this problem you must apply the proccedure shown below:
1. You have that a grapefruit is 8% heavier than an orange and an apple is 10% lighter than the orange. Therefore, let's give a value to the orange as following:
Orange=1 kg
2. Therefore, you have:
Grapefruit=1 kg+(0.08x1 kg)=1.08 kg
Apple=1 kg-(0.1x1 kg)=0.9 kg
3. Therefore, what percentage is the grapefruit heavier than the apple?
%=(0.9/1.08)100-100
%=16.66%
The answer is:16.66%