CCX (Toffoli) gate calculation

Question

I expected |110> since we do

a -> a 
b -> b
c -> ab + c (mod 2)

since x 0 -> 1 and 1+1 = 0 mod 2 we get 110. Why is qiskit returning 011?

Answer 1

This is just because of the qubit ordering. The 0 in the result $|011\rangle$ is the most significant qubit and corresponds to q_2 in the circuit diagram.