If the boy weighs 88kg and it is 10% higher than his normal weight, we can use the following formula to find his normal weight:
Normal weight = Current weight / (1 + 10%)
10% of the boy's weight is 0.10 * 88kg = 8.8kg
So, Normal weight = 88kg / (1 + 8.8kg) = 88kg / 1.10 = 80kg
Therefore, the boy's normal weight is 80kg.