Too odd

Number Theory Level 1

Out of the first 100 positive integers, how many odd primes are there?

Details and assumptions

You may use the fact that there are 25 prime numbers from 1 to 100.


The answer is 24.

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Arron Kau by Arron Kau

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9 solutions

Bodhisatwa Nandi
Oct 1, 2013

Out of the 25 primes number except 2 all other must be prime otherwise any of them would be divisible by 2.

4 Helpful 0 Interesting 0 Brilliant 0 Confused
Aakash Jain
Sep 30, 2013

given that there are 25 primes between 1 and hundred

w.k.t. the only even prime is 2

no. of odd primes between 1 and 100=total primes-even primes=25-1=24

2 Helpful 0 Interesting 0 Brilliant 0 Confused
Ishika Ghosh
Sep 30, 2013

There is only one even prime(2). Given there are 25 primes. Thus there are 24 odd primes.

2 Helpful 0 Interesting 0 Brilliant 0 Confused
Rakhmat Muliawan
Sep 29, 2013

there an even number prime universally, so there are 24 even prime numbers from 1 to 100

1 Helpful 0 Interesting 0 Brilliant 0 Confused

well

Muhammad Yousaf Khan - 7 years, 8 months ago
Vubon Roy
Nov 9, 2014

25-1= 24 because only 2 is a prime even number

0 Helpful 0 Interesting 0 Brilliant 0 Confused
Iranna Hubballi
Apr 24, 2014

there are 25 prime numbers, and we know that only 2 is the even prime number then, 25-1 = 24.

0 Helpful 0 Interesting 0 Brilliant 0 Confused

Since there are 25 prime numbers, and we know that only 2 is the even prime number then, 25-1 = 24.

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the hint is given that there are 25 prime munber(1-100), 2 is the only non-odd number. So there are 24 odd prime number (1-100)

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Arianna Williams
Oct 3, 2013

Their is only one positive integer, which is two so if their are 25 integers between 1 and 100 you can assume that the answer is twenty four

0 Helpful 0 Interesting 0 Brilliant 0 Confused

What do you mean by "There is only one positive integer"? Remember to read what you wrote, to ensure that it is exactly what you are thinking.

Calvin Lin Staff - 7 years, 8 months ago

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