Answer:
The grapefruit is 18% heavier than the apple.
Explanation:
Orange defines the 100% in this situation.
We know that grapefruit is 8% heavier than an orange, so the weight of a grapefruit (in percentage) will be: 100% + 8% = 108%
And an apple is 10% lighter than the orange, then the weight (in percentage) of the apple will be: 100% - 10% = 90%
The difference between the two weights is then:
grapefruit - apple
108% - 90% = 18%
So the grapefruit is 18% heavier than the apple.