Order of Operations in Combined Probability Formula

[brickbreaker]

[original post removed]

[S2000magician]

@brickbreaker

Reading 12 Section 3.1

“For example, consider Ernest and Beatrice Webster, ages 79 and 68, respectively. Their individual probabilities of survival are shown in Columns 3 and 5 of Exhibit 2. Over the next year, Ernest has approximately a 93.6 percent chance of survival, while the younger Beatrice has a 98.3 percent chance of survival.13 The chance of either one of them surviving, however, is greater than either of their individual probabilities of survival. Specifically, the combined probability that either or both survive for the first year is 0.9989 = 0.9355 + 0.9831 − 0.9355 × 0.9831. This figure is represented in Column 6.”

I don’t understand how they came up with a combined probability of .9989. The order of operations in the given formula do not produce that number.

Actually, they do.

Multiplication precedes addition/subtraction, so it’s:

0.9355 + 0.9831 – (0.9355 × 0.9831) = 0.9355 + 0.9831 – 0.9197 = 0.9989