Net Electric Field: Find Magnitude Midway Between 2 Particles

[nothingatall]

Homework Statement

Two particles are fixed to an x axis: particle 1 of charge -1.23 x 10-7 C is at the origin and particle 2 of charge +1.23 x 10-7 C is at x = 15.5 cm. Midway between the particles, what is the magnitude of the net electric field?

Homework Equations

E=kQ/r^2 and/ or E=2kQ/r^2

The Attempt at a Solution

I used the first equation and I got 3.68e5 N/C then I used the second equation because there are two charges and I got 3.93e5 N/C. Both of these answers were marked wrong and I don't know why. Any help? Thanks.

 

[minimark1234]

well your halfway there if you did the math right on both of those. a major concepts of electrodynamics is the rule of superposition, which states that the electric fields at any point is the sum of all the electric fields due to each electric charge effecting your system.