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Prime numbers, Even and Odd

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Intern
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Prime numbers, Even and Odd [#permalink]

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New post 02 Oct 2008, 23:43
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Is there a easy way to solve these kind of question?

How many prime number are there between 100 to 500, Inclusive?

What is the total number of integers between 100 and 500 that are divisible by 3?

What is the total number of integers between 100 and 200 that are divisible by 2?

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Re: Prime numbers, Even and Odd [#permalink]

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New post 03 Oct 2008, 00:19
Yes there is an easy way. Take an example of nos b/w 100 and 300 inclusive which are dividsible by 3?
Take the first and last nos in this range which are divisible by 3
(102 and 300 in this case)
Now take the difference 300-102=198
Divide this by 3,
198/3=66
add 1 to it
66+1=67
Thus, it is (300-102)/3 +1

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Re: Prime numbers, Even and Odd [#permalink]

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New post 03 Oct 2008, 00:37
Thank you so much!!!!

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Re: Prime numbers, Even and Odd [#permalink]

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New post 03 Oct 2008, 00:38
How to determine the number of primes within a given range ?
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Re: Prime numbers, Even and Odd [#permalink]

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New post 03 Oct 2008, 01:21
amitdgr wrote:
How to determine the number of primes within a given range ?


List all the primes and count :-D . If this is the statement, it will be sufficient.

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Re: Prime numbers, Even and Odd [#permalink]

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New post 03 Oct 2008, 01:23
Is there a way to test and determine whether a number is prime or not ?
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Re: Prime numbers, Even and Odd [#permalink]

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New post 03 Oct 2008, 03:10
The easiest & simplest method is to divide the number up to the closet square root of that number.
Ex. Lets determine whether 73 is prime or not. Number close to 73 having a perfect square is 81 and its square root is 9. Now start dividing 73 from 2 to 9. There is no such number between 2 to 9 which divides 73, so 73 is a prime number.
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Re: Prime numbers, Even and Odd   [#permalink] 03 Oct 2008, 03:10
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