The average weight of 16 boys is 15 kg. If the average weight of the first 9 boys is 10 kg and the last 6 boys is 18 kg, then what will be the weight (in kg) of the tenth boy?

Given:
Average weight of 16 boys = 15 kg
Average weight of first 9 boys = 10 kg
Average weight of last 6 boys = 18 kg

Total weight = Average × Number of boys

Solution:
Total weight of 16 boys = 16 × 15 = 240 kg
Total weight of first 9 boys = 9 × 10 = 90 kg
Total weight of last 6 boys = 6 × 18 = 108 kg

Weight of the 10th boy = Total weight − (Weight of first 9 boys + Weight of last 6 boys)
= 240 − (90 + 108)
= 240 − 198

= 42 kg
So, the weight of the tenth boy is 42 kg.

Thus, the correct answer is (b).