Results 1 to 9 of 9

Math Help - Four Eights Problem

  1. #1
    Newbie
    Joined
    Jan 2007
    Posts
    4

    Smile 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
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Global Moderator

    Joined
    Nov 2005
    From
    New York City
    Posts
    10,616
    Thanks
    9
    What does it mean "regular" functions? Functions that has a lot of fiber? Or functions like + - * /?

    ------
    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?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Jan 2007
    Posts
    4
    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
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    9,845
    Thanks
    320
    Awards
    1
    No matter what I do I can't do it with less than five 8s!

    -Dan
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    Jan 2007
    Posts
    4
    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.
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Global Moderator

    Joined
    Nov 2005
    From
    New York City
    Posts
    10,616
    Thanks
    9
    Quote Originally Posted by magnolia_summer View Post
    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.
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Newbie
    Joined
    Jan 2007
    Posts
    4

    Cool

    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
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Super Member
    earboth's Avatar
    Joined
    Jan 2006
    From
    Germany
    Posts
    5,829
    Thanks
    123
    Quote Originally Posted by magnolia_summer View Post
    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:

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

    EB
    Follow Math Help Forum on Facebook and Google+

  9. #9
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    9,845
    Thanks
    320
    Awards
    1
    Quote Originally Posted by earboth View Post
    Hello,

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

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

    EB
    Ooooh! I was so close! (grumbles)

    -Dan
    Follow Math Help Forum on Facebook and Google+

Search Tags


/mathhelpforum @mathhelpforum