Shooting StarProbability puzzles require you to weigh all the possibilities and pick the most likely outcome.
Henry and Gretchen plan on sitting outside to look for shooting stars. They know from experience that if they watch for an hour, they will have a 90% chance of seeing a shooting star. It is a chilly night, though, so Gretchen says, "Let's only stay out for 10 minutes."
Henry says, "I was really hoping to see a shooting star tonight. If we are only out for 10 minutes, we will only have a 15% chance."
Gretchen replies, "Not true. We have a better chance than that."
Is Gretchen right? If so, what is the probability that they see a shooting star?
HintWhat is the probability that they don't see a shooting star over the course of an hour? Ten minutes?
AnswerGretchen is right. The probability that they will see a shooting star is about 32%.
We know that the probability that they don't see a shooting star over the course of an hour is 10%. This is the product of not seeing a shooting star for 6 consecutive 10-minute periods. So if q is the probability of not seeing a shooting star over a 10-minute period, we can say:
0.1 = q^6
q = 0.6813
We know that the probability that they do see a shooting star is just 1 minus the probability that they don't, or 1 - 0.6813, which equals about 32%.
See another brain teaser just like this one...
Or, just get a random brain teaser
If you become a registered user you can vote on this brain teaser, keep track of
which ones you have seen, and even make your own.
Back to Top