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How many prime numbers between 1 and 100 are factors of

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Director
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How many prime numbers between 1 and 100 are factors of [#permalink] New post 30 Apr 2006, 07:12
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 1 sessions
How many prime numbers between 1 and 100 are factors of 7,150 ?

A. One
B. Two
C. Three
D. Four
E. Five

Please explain your approach.
VP
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Re: PS: Factors of 7,150? [#permalink] New post 30 Apr 2006, 08:30
M8 wrote:
How many prime numbers between 1 and 100 are factors of 7,150 ?

A. One
B. Two
C. Three
D. Four
E. Five

Please explain your approach.


Factorize it and get 4 unique factors
2*5*5*11*13
Manager
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Re: PS: Factors of 7,150? [#permalink] New post 30 Apr 2006, 08:31
First, find the prime factorization of 7150. I fear there is
no shortcut for that :(

7150 = 2 * 5^2 * 11 * 13

That's it. You don't have to check any combinations because
the numbers couldn't be prime.

So 2, 5, 11 and 13 and therefore D.

By the way, the condition "between 1 and 100" is useless.
VP
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Re: PS: Factors of 7,150? [#permalink] New post 30 Apr 2006, 08:33
ccax wrote:
First, find the prime factorization of 7150. I fear there is
no shortcut for that :(

7150 = 2 * 5^2 * 11 * 13

That's it. You don't have to check any combinations because
the numbers couldn't be prime.

So 2, 5, 11 and 13 and therefore D.

By the way, the condition "between 1 and 100" is useless.


its handy to have the mulitplication tables by heart....Tough to do it...But it does pay back :-D
Manager
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Re: PS: Factors of 7,150? [#permalink] New post 30 Apr 2006, 18:49
trivikram wrote:
M8 wrote:
How many prime numbers between 1 and 100 are factors of 7,150 ?

A. One
B. Two
C. Three
D. Four
E. Five

Please explain your approach.


Factorize it and get 4 unique factors
2*5*5*11*13


btw, is there a shortcut to know if a number is divisible by 11 and/or 13? In this case 143 is divisible by both. Thanks
VP
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Re: PS: Factors of 7,150? [#permalink] New post 30 Apr 2006, 18:59
shampoo wrote:
trivikram wrote:
M8 wrote:
How many prime numbers between 1 and 100 are factors of 7,150 ?

A. One
B. Two
C. Three
D. Four
E. Five

Please explain your approach.


Factorize it and get 4 unique factors
2*5*5*11*13


btw, is there a shortcut to know if a number is divisible by 11 and/or 13? In this case 143 is divisible by both. Thanks


143 is divisble by 11

Add alternate numbers and subtract one from the other

1+3 = 4
the other alterrnate number is 4
So 4-4 = 0 is divisible by 11

So this is a test for 11 divisibility
Director
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 [#permalink] New post 01 May 2006, 00:43
OA is 'D' (Four)
Great work guys. :)
  [#permalink] 01 May 2006, 00:43
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