Question

Average weight of three students is 40 kg. If the first student is twice the second and the second student is thrice the weight of the third student, then what is the weight of the student with the lightest weight?

Answer 1

1st student's weight = a
2nd = b
3rd = c

therefore, a = 2b and b = 3c
so a = 6c

total weight of the students = 40×3 = 120 kg
so
a + b + c = 120
6c + 3c + c = 120
10c = 120
c = 12 kg
so 3c = 36 kg and 6c = 72 kg

therefore
1st student weighs 72 kg
2nd weighs 36 kg
3rd weighs 12 kg

lightest student is 3rd student who weighs 12 kg.