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prime number

by apex231 » Mon Dec 12, 2011 8:29 pm
If k is a positive integer, is K a prime number?
1) No integers between "2" and "square root of K" inclusive divides k evenly?
2) No integers between 2 and k/2 divides k evenly, and k is greater than 5.
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Source: — Data Sufficiency |
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by rijul007 » Mon Dec 12, 2011 10:07 pm
1) No integers between "2" and "square root of K" inclusive divides k evenly?

let us take any no say 24

approx sq rt of 24 could be 4.8

now wee start from 2 checking for factors

2*12 = 24
3*8 = 24
4*6 = 24
When we check nos after 4.8.. such as 6,8..
the combinations above would repeat

So whenever we need to check whether a no is prime we just need to go till the approx sq rt

aCC to the statement we did the same and didnt get any factors ..
so the No is prime

Sufficient


2) No integers between 2 and k/2 divides k evenly, and k is greater than 5.

The statement doesnt tell us whether the no is divisible by 2 or not

let us say the no is 14
we have checked all the nos b/w 2 and 7 and none of them divide 14

Insuficient


Option A
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