According to the question, the right combination of 2 wires cut (out of the 4 wires ) will defuse the bomb. To find all the possible combinations we using the following formulae;
nCr = n! / r! * (n - r)!
⁴₂C = 4! / 2! * (4-2)!
⁴₂C = 24 / 2 * 2
⁴₂C = 6
There are a possible 6 combinations
Therefore for probability of cutting the right combination of 2 wires is 1/6