Two bodies of mass M and m are placed at a distance ‘2d’.  The force on the body of mass ‘m’. When a mass ‘2M’ is kept midway between them is.

universal gravitation constant=G; mass=m; distance=r; Force=Gm1m2(distance)2 Force on ‘m’ due to 2M isF1=Gm×2Md2  along CB   Force on ‘m’ due to M isF2=Gm×M4d2   along CA∴F=F1+F2=GMmd22+14=94GMmd2   along CA