If the probability of winning a game is 0.7, what is the probability of losing it?

For any event E, P(E) + P(not E) = 1

Let probability of winning a game = P(E) = 0.7

∴ P(winning a game) + P(losing a game) = 1
⇒ P(losing a game) = 1 − 0.7
= 0.3

Thus, the probability of losing a game is 0.3.