A Multiplication Based Logic Puzzle

  • 747 is a composite number.
  • Prime factorization: 747 = 3 x 3 x 83, which can be written 747 = (3^2) x 83
  • The exponents in the prime factorization are 2 and 1. Adding one to each and multiplying we get (2 + 1)(1 + 1) = 3 x 2  = 6. Therefore 747 has exactly 6 factors.
  • Factors of 747: 1, 3, 9, 83, 249, 747
  • Factor pairs: 747 = 1 x 747, 3 x 249, or 9 x 83
  • Taking the factor pair with the largest square number factor, we get √747 = (√9)(√83) = 3√83 ≈ 27.3313007.

747-factor-pairs

It’s Steve Morris’s birthday so I thought I’d make him a cake, but no regular size cake will do. He has been one of my earliest supporters, and I know that sometimes even a level 6 puzzle is just too easy for him. Once he sent out this tweet:

//platform.twitter.com/widgets.js

Admittedly that puzzle was easier than most level 6’s, but recently he tweeted me a puzzle that I have had to start over more than once and still haven’t conquered:

//platform.twitter.com/widgets.js

I think Steve Morris is due for an extra difficult Find the Factors puzzle for his birthday, one that all the numbers from 1 to 16 can be the factors. I’ll wait at least a week before I give any hints to complete it, too. As always, there is only one solution, but it can be found using logic.

747 Birthday Puzzle

Print the puzzles or type the solution on this excel file: 10 Factors 2016-01-18

The possible factors for each clue is given below. Adding 14, 15, and 16 as possible factors really complicates the puzzle!

747 Puzzle Clues

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Now I’ll write a little about the number 747:

747 is a palindrome in base 10. Boeing’s most recognizable airplane also bares that number.

747 can be written as the sum of consecutive numbers five different ways:

  • 373 + 374 = 747; that’s 2 consecutive numbers
  • 248 + 249 + 250 = 747; that’s 3 consecutive numbers
  • 122 + 123 + 124 + 125 + 126 + 127 = 747; that’s 6 consecutive numbers
  • 79 + 80 + 81 + 82 + 83 + 84 + 85 + 86 + 87 = 747; that’s 9 consecutive numbers
  • 33 + 34 + 35 + 36 + 37 + 38 + 39 + 40 + 41 + 42 + 43 + 44 + 45 + 46 + 47 + 48 + 49 + 50 = 747; that’s 18 consecutive numbers

747 is the sum of three squares six different ways. Three of those ways repeat squares.

  • 27² + 3² + 3² = 747
  • 25² + 11² + 1² = 747
  • 23² + 13² + 7² = 747
  • 21² + 15² + 9² = 747
  • 19² + 19² + 5² = 747
  • 17² + 17² + 13² = 747

—————————————

Since today’s puzzle is the biggest puzzle I have ever published, it could be a little difficult just noticing that a factor had been duplicated in the top row or first column. Here is the tweet Steve Morris sent out once he finally solved the puzzle:

//platform.twitter.com/widgets.js

Now after waiting over a week, I now reveal one of the ways to solve this difficult puzzle logically:

747 birthday Logic

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Comments on: "747 Happy Birthday, Steve Morris!" (21)

  1. Wow! Iva, I am truly touched and honoured by your post! I’m amazed you even remembered it’s my birthday. What a lovely gift – a fiendishly hard puzzle to solve 🙂 I will work on it this evening and let you know if I can solve it.
    That GCHQ puzzle took me 3 attempts over 3 days, but I did eventually work it out. Unfortunately it then leads to an even harder set of puzzles that defeated me.
    I’m very proud to be a long-time supporter of Findthefactors, as I think it’s such a cool idea and a great way to practise multiplication facts. I’m glad your blog is getting such well-deserved attention.

    Liked by 1 person

  2. Happy, happy birthday to Steve! What a wonderful way to celebrate someone’s birthday! You’re both awesome, and I’m ever so happy to have you as blog friends. 😀

    Liked by 1 person

  3. […] was also astonished to find that fellow blogger, Iva Sallay, has created a maths puzzle as a birthday gift for me. I’m very much looking forward to trying to solve that […]

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  4. Well this is a really tough challenge. No solution yet …

    Liked by 1 person

    • I won’t have time today, but tomorrow I’ll see how long it takes me to solve it. I designed this puzzle over a month ago so I don’t remember exactly what the logic is to solve it. I promise I won’t peek at my notes of that logic. I predict it will take me at least a couple of hours.

      Liked by 1 person

  5. OK, I officially cannot solve this puzzle!

    Liked by 1 person

    • Let me give you the first piece of logic to solve it. The possible common factors for 80 and 64 are 8 and 16, but the common factor has to be 16 for the following rather complicated reason:
      The 32 in the puzzle must be 4 x 8 or 2 x 16 so it will use either an 8 or a 2.
      22 definitely uses a 2. If 32 and 22 use both 2’s, then 8 = 8 x 1. Otherwise 32 is 4 x 8.
      Therefore, either 32 uses an 8, or 8 uses an 8.
      Either way, an 8 is used so 64 would have to be 4 x 16, not 8 x 8.

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      • As promised, I set the timer to see how long it would take me to solve the puzzle after not looking at it for a month. I didn’t set the timer until after I gave you the first piece of logic so I remembered how to start the puzzle. Also there still were a few things I remembered even after a full month since creating it, but it still took me 26 minutes, 21 seconds to solve the puzzle today. It is a bear.

        Like

  6. Well, a happy birthday to him! Neat.

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  7. OK, yes I got that. Then several more entries fall into place and I deduced that the common factor of 48 and 72 must be 8.

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  8. Then I worked out that 8 must be 1×8.

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  9. Next, I deduce that 84 is 6×14, 45 is 3×15 and the top 48 is 4×12. This means that the common factor of 48 and 72 must be 8!!!!

    Like

  10. Got it! Thanks to Iva for showing me where I was going wrong!

    Liked by 1 person

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