Two point charges are brought closer together, increasing the force between them by a factor of 25. by what factor was their separation decreased? in other words, if r1 is the original separation and r2 is the final separation, what is the ratio r1/r2?

Inelastic is the answer your looking for.

The answer is 4f======since electrostatic force is given by    we let f be the electrostatic force when  r = 1 m    if we let  denote the electrostatic force when the distance is decreased so that r = 0.5m, then    we established earlier that f = kq₁q₂. therefore    the force will now be 4f.