Official Solution: Bunuel
John has a 0.8 probability of eating breakfast with bacon and eggs, and Mary has a probability p of doing yoga in the morning.
If these events are independent, select for
At least one the probability that at least one of these events occurs, and select for
p the probability of Mary doing yoga in the morning that would be jointly consistent with the given information. Make only two selections, one in each column.
Since the events are independent, P(at least one) = P(breakfast) + P(yoga) - P(both). So, we get:
P(at least one) = P(breakfast) + P(yoga) - P(both) =
= 0.8 + p - P(breakfast) * P(yoga) =
= 0.8 + p - 0.8 * p =
= 0.8 + 0.2p
Obviously, P(at least one) must be greater than 0.8, so 0.85, 0.9, or 0.95.
Substituting 0.85 gives p = 0.25, which is absent from the options.
Substituting 0.9 gives p = 0.5, which is present in the options.
Therefore, the correct answer is
p = 0.5, and
the probability of at least one event occurring is 0.9.
Correct answer: At least one
"0.9"\(p\)
"0.5"