A Multiplication Based Logic Puzzle

Archive for May, 2014

133 and Level 6

133 is a composite number. 133 = 1 x 133 or 7 x 19. Factors of 133: 1, 7, 19, 133. Prime factorization 133 = 7 x 19.

  • The divisibility trick for 7 tells us to split 133 into 13 and 3. We double 3 and find the difference between the double and 13. We get 13 (2 x 3)  = 13 – 6  = 7 (an obvious multiple of 7) so 7 is a factor of 133.

133 is never a clue in the FIND THE FACTORS puzzles.

2014-21 Level 6

Excel file of puzzles and previous week’s solutions: 10 Factors 2014-05-26

2014-21 Level 6 Logic

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132 and The Hourglass Is Almost Empty

132 is a composite number. 132 = 1 x 132, 2 x 66, 3 x 44, 4 x 33, 6 x 22, or 11 x 12. Factors of 132: 1, 2, 3, 4, 6, 11, 12, 22, 33, 44, 66, 132. Prime factorization: 132 = 2 x 2 x 3 x 11, which can also be written 132 = 2² x 3 x 11.

Taking the factor pair with the largest square number factor, we get √132 = (√4)(√33) = 2√33 ≈ 11.489

 

When 132 is a clue in the FIND THE FACTORS  1 – 12 puzzles, always use 11 and 12 as the factors.

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This puzzle reminds me of a couple of hour glass scenes from The Wizard of Oz that can be found about the middle of the page here. Yes, I know my hour glass is about the size of an egg timer, but hurry and solve the puzzle! Dorothy’s life could depend on it.

2014-21 Level 5

Excel file of puzzles and previous week’s solutions: 10 Factors 2014-05-26

2014-21 Level 5 Logic

131 and Level 4

131 is a prime number. 131 = 1 x 131. Its only factors are 1 and 131. Prime factorization: none.

How do we know that 131 is a prime number? The square root of 131 is an irrational number approximately equal to 11.45. If 131 were not a prime number, then it would be divisible by at least one prime number less than or equal to 11.45. Since 131 cannot be divided evenly by 2, 3, 5, 7, or 11, we know that 131 is a prime number.

131 is never a clue in the FIND THE FACTORS puzzles.

2014-21 Level 4

Excel file of puzzles and previous week’s solutions: 10 Factors 2014-05-26

2014-21 Level 4 Logic

130 and Level 3

130 is a composite number. 130 = 1 x 130, 2 x 65, 5 x 26, or 10 x 13. Factors of 130: 1, 2, 5, 10, 13, 26, 65, 130. Prime factorization: 130 = 2 x 5 x 13.

130 is never a clue in the  FIND THE FACTORS 1 – 10 or 1 – 12 puzzles.

2014-21 Level 3

Excel file of puzzles and previous week’s solutions: 10 Factors 2014-05-26

A Logical Approach to FIND THE FACTORS: Find the column or row with two clues and find their common factor. Write the corresponding factors in the factor column (1st column) and factor row (top row).  Because this is a level three puzzle, you have now written a factor at the top of the factor column. Continue to work from the top of the factor column to the bottom, finding factors and filling in the factor column and the factor row one cell at a time as you go:

2014-21 Level 3 Factors

129 and Level 2

129  is a composite number. 129 = 1 x 129 or 3 x 43. Factors of 129: 1, 3, 43, 129. Prime factorization: 129 = 3 x 43.

2 + 3 + 5 + 7 + 11 + 13 + 17 + 19 + 23 + 29 = 129, thus 129 is the sum of the first 10 prime numbers.

129 is never a clue in the FIND THE FACTORS puzzles.

2014-21 Level 2

Excel file of puzzles and previous week’s solutions: 10 Factors 2014-05-26

2014-21 Level 2 Factors

128 and Level 1

128  is a composite number. 128 = 1 x 128, 2 x 64, 4 x 32, or 8 x 16. Factors of 128: 1, 2, 4, 8, 16, 32, 64, 128. Prime factorization: 128 = 2×2×2×2×2×2×2 which can be written 128 = 2⁷

128 is never a clue in the FIND THE FACTORS  puzzles.

2014-21 Level 1

Excel file of puzzles and last week’s solutions: 10 Factors 2014-05-26

2014-21 Level 1 Factors

127 and Level 6

127 is a prime number. 127 = 1 x 127. Its only factors are 1 and 127. Prime factorization: none.

How do we know that 127 is a prime number? The square root of 127 is an irrational number approximately equal to 11.27. If 127 were not a prime number, then it would be divisible by at least one prime number less than or equal to 11.27. Since 127 cannot be divided evenly by 2, 3, 5, 7, or 11, we know that 127 is a prime number.

Thinking process using divisibility tricks to prove that 127 is not divisible by 2, 3, 5, 7, or 11:

  • 127 is not even, so 127 is not divisible by 2.
  • 1 + 2 + 7 = 10 which is not divisible by 3, so 127 is not divisible by 3.
  • The last digit of 127 is not 5 or 0, so 127 is not divisible by 5.
  • The divisibility trick for 7 requires us to split 127 into 12 and 7. We double 7 and find the difference between the double and 12. We get (2 x 7) – 12  = 14 – 12 = 2. Since 2 is not divisible by 7, 127 is also not divisible by 7.
  • To perform the divisibility trick for 11 we look at the digits another way: Digits that are in an odd position are in regular type and the digit in an even position is in bold type: 127. We find the sum of the numbers typed in regular type (1 + 7  = 8) and the sum of the number(s) typed in bold type (2) and subtract the smaller sum from the larger sum (8 – 2 = 6). If the difference were a multiple of 11, than the original number would also be a  multiple of 11 (and divisible by 11). Since 6 is not a multiple of 11, we know 127 is not divisible by 11.

Therefore the only factor pair that exists for 127 is 1 x 127, and it is a prime number.

127 is never a clue in the FIND THE FACTORS puzzles.

Spotting the logic needed to begin this Level 6 puzzle should be easier than usual. If you have completed Level 5 puzzles, but have never before attempted a Level 6 puzzle, try this one !

2014-20 Level 6

Excel file of this week’s puzzles and last week’s factors: 12 Factors 2014-05-19

2014-20 Level 6 Logic

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