First Post!

And now that I've actually read this post, I am DEFINITELY going to mess around with this puzzle. We'll see how it goes!

It says you can use decimal points: does that mean you can do things such as ***REMOVED THE ANSWER*** or ***REMOVED THE ANSWER***? If so, then I think I have them all.

Feldman you rock! Although your nine example doesn't work. I have them all now except the 7 answer.

I am a bit tired... what is wrong with the nine example? Can you not use decimal points just in between two digits (ala ***REMOVED THE ANSWER***)? Or can you not use a decimal point directly next to a operator (the ***REMOVED THE ANSWER*** )?

Alright! Sounds like fun. :-)

I've figured out all of them except the one for 7 as well.. Hmm...

I got it!

***REMOVED THE ANSWER***

Just my stupidity. I read your answer as + .9 not / .9 -- OOPS!

I have a different 7 answer... (and a different 9 answer).

I'll post my answers on Thursday (as we need to allow people to enter the contest -- deadline Thursday 3:00 eastern!)

Wow, that was excellent fun! Please let us know if you find out about any other puzzles like this.

I shouldn't have posted my actual answer to the 7 one, though. Could you possibly remove it so that other people have a chance to think about it?

I had the same answer to seven as Adam.

On the 9 example I just did ***REMOVED THE ANSWER***

that 7 solution is awesome, that was the only one I couldn't get

To preserve the fun, I have removed all references to answers from the above posts. OK, y'all, figure it out! And enter the contest on NPR.org when you get your answers... You could win all kinds of cool stuff. Look here for answers on Thursday at 3:00 Eastern!

http://jobs.aol.com/article/onlinecampus/_a/yale-on-0-a-day/20070215175109990001?ncid=AOLCOMMjobsDYNLprim0002

Woot MIT! This article is so true, the OpenCourseWare with Professor Lewin definitely convinced me to apply...

jeez. I got the first few quickly and spent the last fifteen minutes or so trying to figure out the 7 solution. Finally got it :D

awesome.

Yes! got them too! haha. number 7 and 9 did give me the most problems. ironically enough, i did this puzzle in between problems on my partial fraction decomp homework. =P

1, 2, 3, 4, 6 and 9 came easily. The other 3 I'm working on. I know I'm not going to be able to stop until I have the solution.

Madman's Solution:

***REMOVED THE ANSWERS***

Is it legal to put a bar over a decimal point? Like .9999999999999 = .9bar (= 1)?

Madman, took your answers off to preserve the mystery (but all of them look good to me).

Jeff, hmm, interesting thought. I don't know...

I'm, sure i got all the answers except number seven. not to sure bout that one. Otherwise really enjoyed this puzzle.

I got some of them:
***ANSWERS REMOVED***
I will be working in the others.
Mohammed

Yeah I got all of them!!!!!!!!!!!!!!!!!!!!!!! yeah.
I don't know if a Bolivian can participate in the contest but anyway I already sent my answers.
Mohammed

Go and line up for the lottery. [yoohoo] I am not going to sign for that. I don't like to be questioned on the phone. But maybe you like...

***REMOVED THESE ANSWERS***

Sorry , I didn't know we should not post our answers here.

i'd say 7 and 6 were the hardest.

stuck on 4 and 8 =)

Can we move the decimal the other way (ie 7 becomes 70)?

Nevermind, I got it another way =) I'm done!

I do enjoy math puzzles.

Unless they involve geometery. I got jipped in that subject let me tell you. If it wasn't for my lack of geometery skills I could have done decent in the AMC this afternoon, oh well.

Yep, sorry about posting some answers.
Here a newspaper put all the Mondays this kind of puzzle so I have some practice ;) but it still was hard.
If you need any help contact me mohammedmostajo@gmail.com
Mohammed

The 7th was almost definitely the hardest.

I thought 7 wasn't that bad,unless I did it differently =) It took me longest to get 4 and 8, but I felt stupid when I got them because they were pretty obvious =)

OK to post the answers now! The contest is closed...

My answers:

2+7-1=8
(2/2)+7=8
7+3-2=8 OR (7-3)*2=8
2^(7-4)=8
7+2(.5)=8
(7*2)-6=8
7/.7-2=8
7.8+.2=8
(9+7)/2=8 OR 72/9=8

Any other answers?

I was playing with 7(base 7)-2=8 if you agreed that 7 on a base 7 system is equal to a tens place, but nah!

Anyway, I didn't win the contest... Did any of you?

Thanks for playing! This was awesome!

Same answers as you (for 4, I got the first one, adn for 8, I got the second one).

Question, though - Am I just having a "moment", or does (7-3)^2 = 16, not 8?

*and

Oh, and I just realized you probably meant to multiply them =)

OOPS! I did! I'll go back and fix!

How about this answer for #3?

(.7-.2)^-3=8

That's assuming the negative in the exponent is alright, of course.

Another would be

3/.2-7=8

A less rule-bending way to do #8 would be to just add them up seperately.

.8+.2+7

Finally, for #4,

4/(.7-.2)=8

That's all for now, but I'll keep thinking. :-)

Adam, you rock my world... ;)

Question is... did anyone get picked? I didn't. :-(

I thought Adam S.'s variations were awesome. I amused myself on my run today by realizing the problem could be extended a bit. Start w/ 0 instead of 1 and end w/ 13 instead of 9. I've posted my solutions at http://primepuzzle.com/leesnewest/make-8.html but you're not allowed to look until you've given it a shot. Of course, I'm sure Adam'll come up with some alternates.

Lee Bradley

good one - especially 7th one..
why should someone find 7th one tough... is it something related to how the brain computers or analyses it.... whizzing through five or six numbers..
suddenly what happens...neurons loose gigabit ethernet connection and acquire just a megabit EC
what about posts where 5th and 9th were tough.. effective connection between the neurons, how active..
for all math whizzes out there, what should we take care or factors for solving these problems much faster and efficient...or answers for my question is just 'a cool head'?

For all those that remain interested in this stuff, the link I posted in my March 4th note has slightly different content than it did on March 4th. Several of the proposed solutions have been declared illegal and a few alternate solutions have been added.

Also, the correct spelling of the originator of this cool problem is Robert T. Wainwright. This fellow has been around for a while and in the early 70s edited a quarterly newsletter called LIFELINES which was a clearing house for all the discoveries people were making with John Conway's Game of Life.

And, if you liked this one, check out Robert Wainwright's

"Building Twenty"

Using the digits 2, 3 and 4 once and only once, develop mathematical expressions which equal all the whole numbers from one through twenty. You may use any of the following symbols: addition [+], subtraction [-], multiplication [x], division [/], exponentiation [^] as well as decimal points and parentheses as needed.

For example: 1=3+2-4

3+2-4 =1
2*3-4 =2
2+4-3 =3
(3-2)*4 =4
3^2-4=5
3*4/2 =6
(3-0.2)/0.4 =7
(4-2)^3 =8
3^(4/2) =9
2*3+4=10
2*4+3=11
(2^3)+4 or 2^3+4 = 12
(3^2)+4=13
4*3+2=14
3*2/0.4 =15
(4/0.2)-3=17
3*(2+4)=18
4^2+3=19
3+2*5=20

how about 16? got stuck on that...
should be simple...