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Topic: make 100 by using 1, 7, 7, 7, 7
Replies: 41   Last Post: Nov 15, 2007 6:13 PM

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 Kira Yamato Posts: 526 Registered: 7/2/05
Re: make 100 by using 1, 7, 7, 7, 7
Posted: Nov 13, 2007 1:59 PM
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On 2007-11-13 13:51:55 -0500, Kira Yamato <kirakun@earthlink.net> said:

> On 2007-11-13 13:22:13 -0500, Robert Israel
> <israel@math.MyUniversitysInitials.ca> said:
>

>> "Benjamin A. Bartsch" <benjamin.a.bartsch@gmail.com> writes:
>>

>>>
>>> dangerousgam...@gmail.com schrieb:

>>>> So, using only +, -, x, /, and parentheses, and ONLY these numbers:
>>>>
>>>> 1, 7, 7, 7, 7
>>>>
>>>> how can you make 100? Is there more than one solution?

>>>
>>> --> (1/7+7)*(7+7)
>>>
>>> Benjamin

>>
>> Yes, and that's the only solution (up to commutativity).

>
> I'm very curious how you concluded this. Was it by a program that
> tests through all possible combinations?
>
> I tried to write a program too, but I stop when I couldn't quickly find
> a way to list out all possible trees with 7 leaves.

Sorry, I meant 5 leaves. My idea was that each expression can be
represented as a tree where each internal node is one of four operators
+,-,*,/ and the leaves are one of the number 1,7,7,7,7.

--

-kira

Date Subject Author
11/12/07 dangerousgame95@gmail.com
11/12/07 Thomas Nordhaus
11/12/07 amzoti
11/12/07 quasi
11/12/07 dangerousgame95@gmail.com
11/13/07 magidin@math.berkeley.edu
11/12/07 Thomas Nordhaus
11/12/07 quasi
11/12/07 Joshua Cranmer
11/12/07 Raymond Manzoni
11/13/07 William Elliot
11/13/07 amzoti
11/12/07 David R Tribble
11/12/07 Nat Silver
11/12/07 Raymond Manzoni
11/12/07 Raymond Manzoni
11/13/07 Adrian Duma
11/13/07 benjamin.a.bartsch@gmail.com
11/13/07 amzoti
11/13/07 David W. Cantrell
11/13/07 magidin@math.berkeley.edu
11/13/07 David W. Cantrell
11/13/07 magidin@math.berkeley.edu
11/13/07 briggs@encompasserve.org
11/13/07 Robert Israel
11/13/07 Dave Seaman
11/13/07 benjamin.a.bartsch@gmail.com
11/13/07 amzoti
11/13/07 David W. Cantrell
11/13/07 Jan Kristian Haugland
11/13/07 Robert Israel
11/13/07 Kira Yamato
11/13/07 Kira Yamato
11/13/07 Robert Israel
11/13/07 amzoti
11/14/07 Thomas Nordhaus
11/15/07 Michael Press
11/14/07 Michael Press
11/15/07 Kira Yamato
11/15/07 Michael Press
11/15/07 Rick Decker
11/13/07 Raymond Manzoni

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