Date: 8/31/96 at 17:34:15 From: Anonymous Subject: Socks Jack's sock drawer contains 10 blue socks and 12 gray socks. The room is dark and he cannot turn on the light. What is the least number of socks he must take out of the drawer to be certain of each of the following conditions? a. He has a pair of the same color. b. He has a pair of the blue socks c. He has a pair of gray socks. d. He has one pair of each color. I've just looked at it a lot and I can not figure it out. Thank you.
Date: 9/1/96 at 3:36:53 From: Doctor Mike Subject: Re: Socks >a. He has a pair of the same color. Least number = 3, because if the first two do not make a pair, then the third will match one of the first two. >b. He has a pair of the blue socks Least number = 14, because the worst case is he will pick all the grey ones on the first 12 tries, and then he is guaranteed that the next two will be blue. >c. He has a pair of gray socks. Least number = 12, because the worst case is he will pick all the blue ones of the first 10 tries, and then he is guaranteed that the next two will be grey. >d. He has one pair of each color. Least number = 14, following essentially the same logic as (b). He could go for 12 tries and get only grey, and then the next two would be blue. If you select 14 of them to take care of this worst case scenario, then all the other situations would be taken care of also. Another answer would be to pick your socks out the previous evening when you could turn the lights on, in which case the first three answers would be 2 and the answer to d would be 4 (unless you are color-blind). I hope this helps. -Doctor Mike, The Math Forum Check out our web site! http://mathforum.org/dr.math/
Search the Dr. Math Library:
Ask Dr. MathTM
© 1994-2015 The Math Forum