In a class of 39 students there are 26 girls with average weight 42 kg. If the average weight of the whole class is 48 kg, then what is the average weight of the boys in the class ?

60 kg

Total weight of 26 girls = 42 × 26 = 1092 kg

Total weight of 39 students = 48 × 39 = 1872 kg

Total weight of (39 – 26) = 13 boys = 1872 – 1092 = 780

Average weight of boys = 780/13 = 60 kg