Ms. Krump's AgeDate: 10/05/1999 at 00:29:43 From: Amanda Subject: Ms. Krump's age One day in math class Shelly asked, "Ms. Krump, how old are you?" Ms. Krump calmly replied, "This year I'm 3 times as old as my little sister. However, 6 years ago I was 5 times as old as she was." "Well, that doesn't help," yelled Clara. "Sure it does" said Frank. "I don't get it," complained Brian. Ms. Krump said, "Think about it some more and we will see how many of you can guess my age when we have class tomorrow." How old is Ms. Krump? I haven't really tried anything yet because I don't really understand it. If you could get the answer (or the method, if there is one) to me, I would greatly appreciate it. Thanks for your help. Amanda Date: 10/05/1999 at 11:24:48 From: Doctor Rob Subject: Re: Ms. Krump's age Thanks for writing to Ask Dr. Math, Amanda. Pick one of the ages and assign a name to it. Say you pick the younger sister's current age, and call it S (for sister). Then Ms. Krump's age now is 3*S, according to her first statement. Now go back six years. Each person's age is smaller by 6. Ms. Krump's age then was 3*S - 6, and her sister's age then was S - 6. Now you can use Ms. Krump's second statement to set up an equation involving S. This you solve for S, and then 3*S is the answer you seek, Ms. Krump's current age. Suppose you instead pick Ms. Krump's current age, and call it K (for Krump). Then her sister's current age is K/3, according to the first statement. Six years ago their ages were K - 6 and K/3 - 6. Now using the second statement, you can set up an equation involving K. Solving this for K will give you the answer sought. For more about age-type word problems, see the following web page from our Classic Problems collection: Age Word Problems http://mathforum.org/dr.math/faq/faq.age.problems.html - Doctor Rob, The Math Forum http://mathforum.org/dr.math/ Date: 10/05/1999 at 23:22:32 From: Scott Griffin Subject: Re: Ms. Krump's age Thanks a lot for the formula - it really helped! In fact, I even got the answer. Ms. Krump is now thirty years old, and 6 years ago she was 24. 10 * 3 = 30 - 6 - 6 -- -- 4 24 * 6 -- 24 Sincerely, Amanda Date: 10/06/1999 at 09:01:35 From: Doctor Rob Subject: Re: Ms. Krump's age Sorry, Amanda, but that's incorrect. Six years ago she was only *FIVE* times as old as her sister, not *SIX* as you seem to have used. Try again! - Doctor Rob, The Math Forum http://mathforum.org/dr.math/ Date: 10/06/1999 at 10:44:32 From: Scott Griffin Subject: Re: Ms. Krump's age Thank you for telling me that. I guess that I was so happy that I knew how to figure it out, that I didn't even read the paper and went off doing a different thing. However, this time I think that I' ve really got the answer. 12 * 3 = 36 - 6 - 6 -- -- 6 30 * 5 -- 30 Ms. Krump is now 36, and 6 years ago she was 30. Ms. Krump's younger sister is now 12, and 6 years ago she was 6. Date: 10/06/1999 at 11:04:42 From: Doctor Rob Subject: Re: Ms. Krump's age You've got it now - good work! Now do some different ones of the same kind, and you'll show yourself that you understand how to do many problems like that. - Doctor Rob, The Math Forum http://mathforum.org/dr.math/ |
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