Question

Suppose Gabe, an elementary school student, has just finished dinner with his mother, Judy. Eyeing the nearby cookie jar, Gabe asks his mother if he can have a cookie for dessert. She tells Gabe that she needs to check his backpack to make sure k. Gabe cannot remember where he left his backpack, but he knows for sure that he did not complete his bomework and will not be alowed to cat a cookie. Gabe believes his only option is to quickly steal a cookie while his mother is out of the room. Judy then leanves the room to look for Gabe's backpack. Assome that Judy could return at any time in the next 90 seconds with equal probability, For the first 40 seconds, Gabe sheepishly wonders if he will get caught rying to grab a nearby cookie. After waiting and not secing his mother, Gabe decides that he needs a cookie and begins to take one from the jar Assuming it takes Gabe 30 seconds to grab a cookie from the jar and devour it without a trace, what is the probability that his mother returns in time to catch Gabe stealing a cookie?

Answer 1

0.56

Explanation:

What is the probability that his mother returns just in time to catch Gabe stealing a cookie?

The probability of this is the same as 1 minus the probability that Gabe is NOT caught.

- Judy could return at anytime in the next 90 seconds

- Gabe spends the first 40 seconds pondering... time wasted=40secs

- It takes 30 seconds (out of the remaining 50secs) to finish eating a cookie without a trace

- The question says that Gabe was going to do it, so he probably did

Now we're looking for the probability that he gets caught. That is, probability that he does not "successfully" complete the 30secs task within the remaining 50secs.

Remember that each second has an equal probability of being the second that Judy comes back in. The latter of the 90 seconds does not carry a higher probability!

So the probability of catching Gabe (despite the 30secs it takes to complete his task) is 50/90 which is equal to 0.56