1. The problem statement, all variables and given/known data The diagram shows two charges, +4 μC and –16 μC, 120 mm apart. What is the distance from the +4 μC charge to the point between the two charges where the resultant electric potential is zero? A 24mm B 40mm C 80mm D 96mm 2. Relevant equations potential equation 3. The attempt at a solution 1. The problem statement, all variables and given/known data The correct answer is a 24mm I get that we could simply use a 1:4 ratio and therefore r must be a fifth of the way from the 4 micro coulomb charge However when I try and equate the formula and solve algebraicaly I seem to get the wrong answer if I put in the sign of the charges. So my question is why do we just use the magnitude of the charges?