The average weight of 45 boys in a school is 50 kg. If the weight of 5 girl students is added, the average is reduced by half-a-kilogram. What is the average weight in kg of the girl students ?

Total weight of 45 boys = 45 × 50 = 2250 kg. After adding 5 girls, total students = 50 and new average = 49.5 kg (reduced by 0.5 kg). New total weight = 50 × 49.5 = 2475 kg. Therefore, total weight of 5 girls = 2475 - 2250 = 225 kg. Average weight of girls = 225/5 = 45 kg. Key distractor: 44.5 kg might come from incorrectly subtracting instead of adding.