The mass of a boy is 50 kg on the Earth, then what will be his weight on the Moon?
 $(Taking \text{g}=10{\text{m/s}}^{\text{2}})$

We know the mass of the boy
$\text{m}=50\text{kg}$ 
First, let's calculate his weight on the earth which is given by:
W_e= mg
Substituting the values,
$\therefore {\text{w}}_{\text{e}}=50\times 9.8=490\text{N}$
We know that the gravitational pull of the moon is 6 times weaker than the gravitational pull of the earth. Therefore, the weight of the boy on the moon will be 1/6th of the weight on the earth.

$\therefore {\text{w}}_{\text{m}}=\frac{{\text{w}}_{\text{e}}}{\text{6}}$

${\mathrm{W}}_m=\frac{490}{6}$

${\text{w}}_{\text{m}}=81.6\text{N}$