A body weighs 200 N on the surface of the earth. How much it weigh half way down to the centre of the earth ?

Acceleration due to gravity at a depth d from surface of earth 
$g^{\prime }=g\left(1-\frac{d}{R}\right)$ ....(1)
Where g = acceleration due to gravity at earth's surface 
Multiplying by mass 'm' on both sides of (1)
$⟹m{g}^{\prime }=mg\left(1-\frac{d}{R}\right)Here,\left(d=\frac{R}{2}\right)$
$=200\left(1-\frac{R}{2R}\right)=\frac{200}{2}=100N$