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prime number questions

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prime number questions

by ijinusean » Sun Apr 15, 2007 12:14 pm
S is the sum of 1 to 30 inclusive, what is the greatest prime number in S?

Can someone help?
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by Tame the CAT » Sun Apr 15, 2007 2:31 pm
S = 15(30+1) = 450

The prime factors of 450 are 2, 3, 3, 5, 5

So, the answer should be 5.
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by ns88 » Sun Apr 15, 2007 3:09 pm
sum of all integers to n =n(n+1)/2

=30*31/2=465

find greatest prime factor by diving by the least

i'll use 3

465/3= 155

next prime is 5

155/5= 31

can't divide any further, ans = 31
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by Cybermusings » Mon Apr 16, 2007 3:07 am
ns88's answer is the right one
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by RAGS » Tue Apr 17, 2007 8:38 am
The question should say Greatest Prime factor in S
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