# Sum of probabilities

If you toss a coin, the probability of obtaining a head is and the probability of obtaining a tail is also .

P (head) + P (tail) =

If we choose a letter at random from the word 'SUMS', the probability of obtaining the letter 'S' is , the probability of obtaining the letter 'U' is , and the probability of obtaining the letter 'M' is .

P(S) + P(U) + P(M) =

Remember that the sum of the probabilities of all possible outcomes is 1.
Question

The probability that I am late for work on any morning is . What is the probability that I am not late for work?

There are two possible outcomes - being late and not being late. The sum of their probabilities must add up to , so the probability of not being late is: