Check the basic definition of probability, then find out how a complicated problem like "the probability that at least one is ~" becomes much easier by flipping it into a complementary event (1โP).
Probability is a number representing how likely something is to happen. It's calculated as the share our desired outcome takes up among every possible outcome, and it always comes out between 0 (will never happen) and 1 (will definitely happen).
A complementary event is the probability that something does not happen. Since the probability of an event and its complement always add up to 1, P(complement)=1โP(event) holds. A problem like "the probability that at least one is ~" often has too many cases to count directly โ but flip it around and find "the probability that none are ~" instead, then subtract from 1, and it becomes much simpler.
Probability shows up constantly in real life too โ the chance of rain in a weather forecast, the odds of winning the lottery. Switch between the tabs and work through basic probability, then complementary events, in order.