Let us assume that a 50 gf weight produces an anticlockwise moment about the middle point ( 50 cm ).

Now, if a weight of 100 gf produces a clockwise moment about the middle point and d cm be the distance from the middle.

As we know, the principle of moments states that

Anticlockwise moment = Clockwise moment.

50 g f × 50 cm = 100 gf × d cm

⇒ d = 50 × 50\over 100 = 25 cm

Therefore, a weight of 100 gf will be suspended at a distance of 25cm to keep the ruler balanced.