posted by mark .
2 objects are .25m apart and exert a force of 2.5x10^-10 N on each other. Thier total mass is 4 kg. what is the mass of each?
Apply Newton's Universal Law of Gravity and solve for M1*M2.
F = 2.5*10^-10 = G M1*M2/(0.25)^2
Once you know M1*M2 and M1 + M2 (= 4 kg), you can solve for M1 and M2 separately.