A Four Product

The product of any 4 consecutive integers must be divisible by _________ . \text{\_\_\_\_\_\_\_\_\_}.

7 8 9 10

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3 solutions

Anandmay Patel
Oct 10, 2016

We use the fact that if a b a|b and b c b|c , then a c a|c .

The product of any four consecutive integers is divisible by 4 ! = 24 4!=24

So,let P P be the product of the four consecutive integers,then: 8 24 8|24 and 24 P 24|P .therefore, 8 P \boxed{8|P}

This is a good start. However, your explanation has a slight gap.

  1. Can you explain why "The product of any four consecutive integers is divisible by 4!"?

Keep writing more solutions and you will get the hang of this!

Calvin Lin Staff - 4 years, 8 months ago

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Sure Sir.I will soon include the proof of that statement in my answer when i get free.[Also the proof is so long(to write the generalization),so i'll write when i get free]

Anandmay Patel - 4 years, 8 months ago
Esp Ter
Oct 14, 2016

Out of the four numbers, two of the numbers are even. Of those two numbers exactly one is a multiple of 4. So 8 will divide their product.

Viki Zeta
Oct 10, 2016

We know product of 3 consecutive numbers is divisible by 8 8 , therefore

( x 1 ) ( x ) ( x + 1 ) 0 m o d 8 ( x 1 ) ( x ) ( x + 1 ) ( x + 2 ) 0 × ( x + 2 ) m o d 8 ( x 1 ) ( x ) ( x + 1 ) ( x + 2 ) 0 m o d 8 (x-1)(x)(x+1) \equiv 0 \mod 8 \\ (x-1)(x)(x+1)(x+2) \equiv 0 \times (x+2) \mod 8 \\ \boxed{\therefore (x-1)(x)(x+1)(x+2) \equiv 0 \mod 8}

The initial premise is only true if the first number is even. For example, 3x4x5=60, which is not divisible by 8.

Anthony Holm - 4 years, 8 months ago

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