JEE Advance - Mathematics (1984 - No. 5)
If $$M$$ and $$N$$ are any two events, the probability that exactly one of them occurs is
$$P\left( M \right) + P\left( N \right) - 2P\left( {M \cap N} \right)$$
$$P\left( M \right) + P\left( N \right) - P\left( {M \cap N} \right)$$
$$P\left( {{M^c}} \right) + P\left( {{N^c}} \right) - 2P\left( {{M^c} \cap {N^c}} \right)$$
$$P\left( {M \cap {N^c}} \right) + P\left( {{M^c} \cap N} \right)$$