I'm stuck on what I think should be a fairly easy question. The question is that there are three charged particles in a line, equidistant (distance L) from each other. From left to right, we'll call them 1, 2, and 3. 1 and 2 are fixed in place, but 3 is free to move. However, the net charge (q) of 1 and 2 on three is keeping 3 in equilibrium. I'm supposed to find the ratio of the charge on 1 to the charge on 2. I figured that basically, that means that q1q3/(2L)² = q2q3/L² . So I end up with the ratio being q1/q2 = 4/1 . But I know that is the wrong answer. So where am I going wrong? Any tips would be appreciated.