Dear Lois:It's getting near the end of school, and my teacher decides to take up probability. I understood the part about flipping coins, but now I'm lost. If I don't get help soon, I'm probably going to fail math for the quarter. Help! Sam
Dear Sam:Let's work on probability from a practical standpoint. Let's say it's 7:45 A.M. The tardy bell rings at your school at precisely 8:00 A.M., and you still have to finish dressing, brush your teeth, and run three blocks to school.
In your semidark bedroom, you pull on a pair of khakis and a red shirt. Now you need socks. It would be nice if your socks matched your other clothes, but at this point fashion is your least concern. You jerk open your sock drawer. It is not a pretty sight. Despite the fact that your mom has told you a thousand times to roll up your socks in pairs before you stuff them in the drawer, your socks are all separated and jumbled together.
You put your hand in the drawer, hoping that your little brother's hampster hasn't taken up residence in the jumble of socks. You wonder, "Just how many socks will I have to pull out of here before I find a pair?
Fortunately, you have only three colors of socks--white, red with blue spots, and yellow with purple stripes. You reach into the drawer and pull out--
Now if the second sock you pull out is a red sock with blue dots, you'll have a pair and can quit. You reach into the drawer, and pull out--
No pair yet. But just think, if the next sock is either red or yellow, you're in business. So you reach in the drawer a third time and pull out--
Now the good news is, no matter what color sock you pull out next, you'll have a pair. It will be either red, or yellow, or white, and so it will match one of the socks you already have. You reach in a fourth time, and you pull out--
So you see, Sam, if you have only three possibilities when it comes to sock color, you can pull out a pair of socks in, at most, four pulls. The only problem is you take your chances on your socks matching your other clothes. I mean, a red shirt, khakis, and yellow socks with purple stripes is not going to get you the best dressed award. If you want to learn about the probability of coming up with socks that match your shirt, you'll have to read Issue 26: Sock Drawer 2.
Well, matching clothes or not, you'd better get a move on. Remember, the tardy bell rings at your school at precisely 8:00 A.M., and you still have to finish dressing, brush your teeth, and run three blocks to school.
Good Luck! Lois
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