Take the 2-minute tour ×
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

Using only four 8's and only addition, subtraction, multiplication, and division.. how can you come up with the number 24? You may use fractions and decimals! But remember, you can ONLY USE four 8's

share|improve this question
3  
I presume you don't like sqrt? Else $8+8+\sqrt{8*8}$ –  Ross Millikan Dec 10 '10 at 4:19
5  
8 + 8 + 8 and then I don't even need the fourth one, thus my solution is presumably 75% more efficient than the intended one! –  MatrixFrog Dec 10 '10 at 4:20
4  
Wouldn't it be 25% more efficient? –  Kevin Brown Dec 10 '10 at 4:28
3  
@Kevin and @MatrixFrog: Efficiency should be measured proportional to the reciprocal of the number of 8s required. MatrixFrog's solution is 33.3% more efficient. Or 25% less inefficient. –  Jonas Meyer Dec 10 '10 at 5:35
4  
This uses only four eights: 8 + 8 + 8 + 8 - 7 - 1 ;-) –  shuhalo Dec 10 '10 at 11:26

3 Answers 3

up vote 7 down vote accepted

$ 88 - (8 \cdot 8 ) $

Much easier with five 8's:

$ 8(8+8+8)/8 $

:)

share|improve this answer
3  
But didn't he say "separate 8's" in the first comment? :) –  J. M. Dec 10 '10 at 8:19
    
I think this is the only solution... –  Kevin Brown Dec 11 '10 at 20:17

I usually recommend RIES for this sort of problem.

share|improve this answer
    
Great stuff; I wish there was an online version of ries though. –  J. M. Dec 10 '10 at 4:44
    
Unfortunately, it would probably find MatrixFrog's solution. –  Ross Millikan Dec 10 '10 at 5:02
    
@J. M.: I've considered doing that myself... haven't gotten around to it, though. –  Charles Dec 10 '10 at 18:24
    
@J.M.: Robert has finally put it online! mrob.com/pub/ries –  Charles Jul 26 '13 at 18:38

The 24game solver found here couldn't find any solutions with 4 8s. I don't think the software uses decimals to create 8.8 etc but its hard to see how that path leads to a solution. The other solution is as friedo suggests (88-8*8).

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.