At a junction in a circuit, currents of $3$ A and $2$ A flow into the junction and a current of $4$ A flows out along one wire. What is the current in the remaining wire?

By Kirchhoff's current law, total current in equals total current out: $3 + 2 = 4 + I$, so $I = 1$ A flowing out. Adding all three given currents gives 9, which ignores direction.