Answer:
54 kg
Step-by-step explanation:
x - regular boy
y - special boy who's weight we're counting
The mean mass of 5 boys:
(4x+y)÷5=62
The mean mass of 4 boys:
4x÷4=64
x=64kg
the mass of y boy:
(4×64+y)÷5=62
(256+y)÷5=62 |×5
256+y=310
y=310-256
y=54