Thread: Four Eights Problem

Hi,

One of my students had a math assignment to complete. First it was a four fours puzzle -- which he was able to do and now the same idea with four eights. He has found all of the answers except how to make four 8s into 13. They are only allowed the "regular" functions, nothing advanced--sorry if that is ambiguous. Could someone please help? I am his English teacher and we really had a fun time with the problems in after school tutoring, but it bothers me that we could not answer one.

Thank you in advance.

8888 === 13 HOW??????

Magnolia

What does it mean "regular" functions? Functions that has a lot of fiber? Or functions like + - * /?

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My own question. These puzzles that ask to express something in terms of something can they be solved by Galois theory? Becuase what we are really cosidering is are all the premutations, which is similar to the classical approach of solution by radicals, by looking at all the premutations. Anybody have any idea?

Ha Ha. Not functions that have a lot of fiber. Functions such as +,-,/,*, and square root. We did use a factorial to solve one of the four fours, but we weren't really sure it was allowed. The rest were solved using only the functions listed above, plus using the 8's as 88 or .8 is also allowed.

Magnolia

No matter what I do I can't do it with less than five 8s!

-Dan

How about this?

sq root(8+8)/.8 +8 =13

works out to sq root(16) =4/.8 = 5 + 8= 13

That seems ok to me, but I don't have a good calculator to check my brain.

Originally Posted by magnolia_summer

How about this?

sq root(8+8)/.8 +8 =13

works out to sq root(16) =4/.8 = 5 + 8= 13

That seems ok to me, but I don't have a good calculator to check my brain.

It works.
But you used "irregular" functions.

You are too much. I should go "English Teacher" on you and correct your typographical errors, but I liked the "irregular" picture so I am going to bed now.

A big thank you to everyone who viewed or replied to this. I think I was also able to take the "factorial" out of the other one that was hard--A four fours for 19.

Thanks again!

Magnolia

Originally Posted by magnolia_summer

Hi,

One of my students had a math assignment to complete. First it was a four fours puzzle -- which he was able to do and now the same idea with four eights. He has found all of the answers except how to make four 8s into 13. They are only allowed the "regular" functions, nothing advanced--sorry if that is ambiguous. Could someone please help? I am his English teacher and we really had a fun time with the problems in after school tutoring, but it bothers me that we could not answer one.

Thank you in advance.

8888 === 13 HOW??????

Magnolia

Hello,

if you are allowed to use cubic roots then this could be a solution:

$\displaystyle \frac{88}{8}+\sqrt[3]{8}=11+2=13$

EB

Originally Posted by earboth

Hello,

if you are allowed to use cubic roots then this could be a solution:

$\displaystyle \frac{88}{8}+\sqrt[3]{8}=11+2=13$

EB

Ooooh! I was so close! (grumbles)

-Dan