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| thyristor |
 Posted: Tue Apr 08, 2008 12:08 pm Post subject: Math-problem |
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Forum Freshman
Joined: 11 Feb 2008
Posts: 66
Location: Sweden
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Here's an easy problem. See if you can solve it!
A man asks his neighbour how old her three daughters are. She says that the product of their ages is 36 and that the sum of them is the man's number on his house.
The man says he needs more information and his neighbour then says that her eldest daughter plays football.
How old are her daughters? |
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| sunshinewarrior |
| Posted: Wed Apr 09, 2008 3:09 am Post subject: |
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Forum Ph.D.
Joined: 26 Sep 2007
Posts: 837
Location: London
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Unless girls are banned from football before the age of 7 you have two options:
1. Twins of 2 and an older sister of 9 (Sum = 13)
2. Girls of 2 and 3 and an older of 6 (Sum = 11)
On balance I'd go for option 2 on the grounds that enough people are superstitious enough not to have the number 13 as their house number... |
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| thyristor |
| Posted: Wed Apr 09, 2008 3:37 am Post subject: |
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Forum Freshman
Joined: 11 Feb 2008
Posts: 66
Location: Sweden
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Nice point, but unfortunately wrong.
The three girls can be of the ages 1,1,36 1,2,18 1,3,12 1,4,9 1,6,6
2,2,9 2,3,6.
The sum of these ages are 38,21,16,14,13,13 and 11.
Since the man knows his own house number he to be able to know their age know but there are two with the sum 13. When his neighbour then says that her eldest daughter plays football he knows that she can't have two girls of the same age that are older than the last one and therefore it must be 2,2,9.
_________________
373 13213-mbm-13213 373 |
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| sunshinewarrior |
| Posted: Wed Apr 09, 2008 4:10 am Post subject: |
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Forum Ph.D.
Joined: 26 Sep 2007
Posts: 837
Location: London
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| thyristor wrote: |
Nice point, but unfortunately wrong.
The three girls can be of the ages 1,1,36 1,2,18 1,3,12 1,4,9 1,6,6
2,2,9 2,3,6.
The sum of these ages are 38,21,16,14,13,13 and 11.
Since the man knows his own house number he to be able to know their age know but there are two with the sum 13. When his neighbour then says that her eldest daughter plays football he knows that she can't have two girls of the same age that are older than the last one and therefore it must be 2,2,9. |
Cool! |
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| Harold14370 |
| Posted: Wed Apr 09, 2008 4:34 am Post subject: |
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Forum Professor
Joined: 13 Apr 2007
Posts: 1263
Location: Pennsylvania
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| One of the twins is a little older than the other. |
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| thyristor |
| Posted: Wed Apr 09, 2008 9:40 am Post subject: |
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Forum Freshman
Joined: 11 Feb 2008
Posts: 66
Location: Sweden
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What do you mean?
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373 13213-mbm-13213 373 |
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| serpicojr |
| Posted: Wed Apr 09, 2008 10:05 am Post subject: |
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Forum Ph.D.
Joined: 17 Jul 2007
Posts: 871
Location: JRZ
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| Harold's saying, in any pair of twins, one is older. So this woman could be talking about an older twin when saying the oldest one plays soccer. |
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