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

Correct option is D. 100N
Acceleration due to gravity at a depth d from the surface of earth
g'=g(1-d/R) (1)
Where g = acceleration due to gravity at earth's surface
Multiplying by mass 'm' on both sides of (1)
=> mg' = mg(1-d/R)
Here,
(d = R/2)
= 200(1 - R/(2R)) = 200/2 = 100N