Question

The average weight of 10 oarsmen in a boat is increased by 1.5 kg when one of the crew who weighs 58 kg is replaced by a new man. Find the weight of the new man.

Answer 1

If you want to increase the average weight of 10 people by by 1.5kg, you are in other words, trying to increase the total weight of the people by 15kg (10 * 1.5 =15).
So, the new guy needs to be 15kg heavier than the 59kg person. That means that the weight of th new guy would be 73kg (58 + 15 = 73).

Solution 2:
Let the average weight of the ten people at the start be x kg.
Let the new guy's weight be y kg.

So, we get:
10x - 58 = 10 (x+1.5) - y
10x - 58 = 10x + 15 - y
-73 = -y
y = 73

Therefore, the new guy's weight is 73kg.