Which of the following choices may represent the probability of an event occurring? (A) Negative 0.7, (B) 1.3, (C) 14 percent, or (D) 197 percent.
First, let’s think about what we know about probability. The probability of an event occurring is equal to the number of ways that event can occur over the total possible outcomes. And the probability will range anywhere from zero to one, where a probability of zero is impossible and a probability of one is certain. But sometimes we represent these probabilities as percents. And when we do that, the range of probabilities is zero percent to 100 percent, where zero percent is impossible and 100 percent is certain.
Why wouldn’t we have values past one or past 100 percent? Because we wouldn’t have anything where we are more than certain. If we’re certain it’s going to happen, it will happen, and there’s no probability past one. For those same reasons, we don’t have negative probabilities. If it’s impossible for something to happen, it has a probability of zero, and there’s nothing to the left of that zero.
This means we can eliminate negative 0.7 as we never have a negative probability. We can eliminate 1.3 because it’s greater than one. And we can eliminate 197 percent because it’s a percentage that’s larger than 100 percent. And that leaves us with 14 percent. 14 percent does fall within the range of normal probability.