The probability that a new ballpoint pen writes poorly (or does not write) is 0.11.

The probability that a new ballpoint pen writes poorly (or does not write) is 0.11. A customer in a store chooses one ballpoint pen. Find the probability that this pen writes well.

Solution.

The sum of the probabilities of all possible events is 1. We have only two possible events: the pen writes poorly, the pen writes well. This means that the probabilities of these two events add up to 1:

P (pen writes well) + P (pen writes poorly) = 1

P (pen writes well) = 1 – P (pen writes poorly) = 1 – 0.11 = 0.89

Answer: 0.89.