Originally Posted by CinderBlockFist
OK, first i had particle1 had 1 charge, and neutral particle 3 had +0.5, and 0.5 charge (since it is the same size as particle 1). When they touch, I added up the charges and divided by two, since the charges would distribute equally, so both end up w/ 0.75 and +0.25 charge.

Just worry about the  charge. + charge is a deficit or lack of  charge.
Sphere 1 has charge 1. S3 has 0 charge. When s3 touches it, charges flow so that the electrical potentials are equal. Since they are identical spheres, this means that each sphere has the same charge. So s3 and s1 each have 1/2 charge. The same thing happens when s3 touches s2. The net charge (+1/2) is distributed equally between s2 and s3 so each charge ends up with +.25.
So you end up with s1 having .5 charge and s2 having a + .25. Since the coulomb force is proportional to the product of the charges, the new force will be: F' = .125 F
AM