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Master | Next Rank: 500 Posts
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by shahdevine » Mon Aug 31, 2009 12:23 pm
What is the greatest value of n such that 7^n is a factor of 50! ?

a)8
b)7
c)6
d)3
e)2

oa after discussion. is there a fast way to do these types of problems?
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by praky_rules » Mon Aug 31, 2009 12:39 pm
7 is a prime number....50! has multiples of seven that include 7,14,21,28,35,42,49 =>7^8 is a factor...(note 49 =7^2). So (a)
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by rish » Mon Aug 31, 2009 12:39 pm
IMO A

50! contains 7 multiples of 7 i.e 7,14,21,28,35,42,49
but 49 is 7*7

so 7^8
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by kaulnikhil » Mon Aug 31, 2009 12:41 pm
A 8
it will be 7 * 14 *21 *28 *35 *42 *49
note 49 has 2 sevens
so 8
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by tohellandback » Mon Aug 31, 2009 7:35 pm
It's basically asking how many 7's are there in 50!

answer is:
50/7 +50/49
= 7+1=8
answer A
The powers of two are bloody impolite!!
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