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Math opportunity.

coolgunguycoolgunguy Senior MemberPosts: 6,610 Senior Member
As a 'make work' sort of assignment, the boy child brings home a twenty question brain teaser. The rules are as follows: Using only the digits 4, 7, 9 & 9, and using any operations necessary, come up with the numbers 1-20. He did pretty good on his own, and I helped with a few...but we can't seem to come up with any way to make 19.

Any ideas?

The teacher did say that some of the problems may be unsolvable, but after working through the others, I feel like this answer is right there in plain sight just waiting for us to realize we were looking at it the whole time.


No, I'm not doing his work for him, but I don't mind helping him either. This was more or less "Do what you can"....
"Bipartisan" usually means that a bigger than normal deception is happening.
George Carlin

Replies

  • NNNN Senior Member Posts: 24,705 Senior Member
    4 divided by 4 = 1 +9+9 = 19
    Shut up-----KAREN; OK Cynthia
  • BigslugBigslug Senior Member Posts: 8,248 Senior Member
    Can't help you - most of my higher math starts from the Prime Conversion: One pound = 7,000 grains.
    WWJMBD?

    "Nothing is safe from stupid." - Zee
  • JerryBobCoJerryBobCo Senior Member Posts: 7,927 Senior Member
    How about 4*7-9?
    Jerry

    Gun control laws make about as much sense as taking ex-lax to cure a cough.
  • coolgunguycoolgunguy Senior Member Posts: 6,610 Senior Member
    NN wrote: »
    4 divided by 4 = 1 +9+9 = 19
    JerryBobCo wrote: »
    How about 4*7-9?


    Sorry, no joy, have to use 4 once, 7 once, and 9 twice. Like I said, it may not be possible, but my gut tells me it is. He worked out fifteen of the numbers on his own, got another four with guidance, but I'm afraid I've helped as much as I can without getting help of my own.

    We've used both the square roots of nine and four, we've used exponents...for example: (9/9) to the 47th power = 1. The numbers can be used in any fashion, but only those four numbers can be used. Another example...(I'm not sure how to get square root brackets on the confuser, but you'll get what I'm doing) Square root of 4 (2) times the square root of 9 (3) times the square root of 9 (3) minus 7 = 11.
    "Bipartisan" usually means that a bigger than normal deception is happening.
    George Carlin
  • coolgunguycoolgunguy Senior Member Posts: 6,610 Senior Member
    How about 4*7 -(sqrt (9) * sqrt (9))



    Well, I said I felt like the answer was staring me in the face all along...:bang:

    Thank you Chris!
    "Bipartisan" usually means that a bigger than normal deception is happening.
    George Carlin
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