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pythagoras123

The product of n whole numbers 1 x 2 x 3 x 4 x ... x (n-1) x n, has twenty-eight consecutive zeros. Find the largest value of n.

  • 2 years ago
  • 2 years ago

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  1. experimentX
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    what are zeros??

    • 2 years ago
  2. pythagoras123
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    "0". This is a zero. Consecutive zeros are zeros that appear consecutively, i.e. The product of 10 x 10x 10 has 3 consecutive zeros (1ooo)

    • 2 years ago
  3. FoolForMath
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    It's somewhat tedious to explain the whole thing. One interesting observation is there would be only trailing zeroes.

    • 2 years ago
  4. experimentX
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    @ffm i'll try before you

    • 2 years ago
  5. pythagoras123
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    Just tell me how you work it out, or the solution/methodology. The answer is not so important.

    • 2 years ago
  6. experimentX
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    i think between 1 and 10, you will have 2 zeros.

    • 2 years ago
  7. FoolForMath
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    I have used binary search along with the usual De Polignac's formula (just) twice to yield 124 as the answer. Ref: http://en.wikipedia.org/wiki/De_Polignac%27s_formula

    • 2 years ago
  8. FoolForMath
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    "Consecutive zeros are zeros that appear consecutively, i.e. The product of 10 x 10x 10 has 3 consecutive zeros (1ooo)" You haven't understood the problem.

    • 2 years ago
  9. experimentX
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    sorry, 139

    • 2 years ago
  10. experimentX
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    @ffm is it correct??

    • 2 years ago
  11. FoolForMath
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    33 for 139.

    • 2 years ago
  12. FoolForMath
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    I have posted the correct answer.

    • 2 years ago
  13. experimentX
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    ah ... where did i screwed up??

    • 2 years ago
  14. pythagoras123
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    @FoolforMath, how did you manage to get 124?

    • 2 years ago
  15. experimentX
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    looks like my theory screwed up from here http://www.wolframalpha.com/input/?i=30%21%2F20%21&dataset=&equal=Submit

    • 2 years ago
  16. experimentX
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    3 zeros ,,,?? how 25*22 = 00 => two zeros were coming from here. so all the factors of 100 or 1000 or 10000 ... were causing problem for my idea.

    • 2 years ago
  17. experimentX
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    1-10 : 2 zeros 10-20: 2 20-30: 3 (25 is factor of 100) 30-40: 2 40-50: 3 (50 is factor of 100) 60-60: 2 60-70: 2 70-80: 3 (at some point 75 will give two zeros) 80-90: 2 90-100: 3 (100 itself gives two) ----------------------- so from 0 to 100 we have: 24 zeros 100-110: 2 110-120: 2 ----------------------- I guess that would give 28 zeros screw you ---> minions of 100

    • 2 years ago
  18. experimentX
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    the answer was n = 120

    • 2 years ago
  19. Aron_West
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    The largest power of 5 dividing n must be 5^28.Now use De Polignac's Formula.

    • 2 years ago
  20. eliassaab
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    120! = 6689502913449127057588118054090372586752746333138029810295671352301633557244962989366874165271984981308157637893214090552534408589408121859898481114389650005964960521256960000000000000000000000000000 Of course you need an analytic proof of that using 2 and 5.

    • 2 years ago
  21. eliassaab
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    Should the question be, find the smallest n to achieve that?

    • 2 years ago
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