The probability of a defective calculator is 10 percent (p = 0.10). If 10 calculators are selected at random, the probability of 3 or more calculators being defective is
P (3 or more calculators being defective) = 1 – P (less than 3 calculators being defective)
In other words, the probability of at least three calculators being defective is the opposite of the probability that fewer that three calculators are defective.
This means that the probability of three or more calculators being defective is equal to one minus the probability that fewer than three calculators are defective.