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Integers- long multiplications?

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Integers- long multiplications?

by vivibcn » Sun Oct 21, 2012 8:49 am
If the number x is equal to the product of the n first positive integers (1, 2, 3, ... n), what is the minimum value of n such that the last six digits are equal to 0?

a. 20
b. 25
c. 30
d. 35
e. 40

Can you help me out? Multiplying is too long, isn't there a faster method?[/u]
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by sanrisenew » Sun Oct 21, 2012 10:56 am
While multiplying consecutive integers if 5 meets 2 it creates a zero , next zero is in 10, next is in 15 and so on .For 6 zeroes 5,10,15,20,25( 25 will create 2 zeroes) therefore we have to multiply upto 25.
Ans. b
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