All possible two factor products formed from the numbers 1,2,3,4.... 200. The number of factors out of the total obtained which are multiples of 5 is?

a. 5040

b. 7180

c. 8150

d. none of these

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- Oct 10th 2012, 08:51 AMswordfish774counting problem
All possible two factor products formed from the numbers 1,2,3,4.... 200. The number of factors out of the total obtained which are multiples of 5 is?

a. 5040

b. 7180

c. 8150

d. none of these - Oct 10th 2012, 09:04 AMPlatoRe: counting problem
- Oct 10th 2012, 09:37 AMswordfish774Re: counting problem
hahaha!

I didnt understand the question, what does number of factors mean

non-multiples of 5 n 160 , multiples of 5 m 40 so, 160C1*40C1

and multiples of 5 n * muliples of 5 so 40C2

so 7180. but there is double counting, how do i remove that?

why do you say 'this is not a homework service'? i use it to solve doubts and verify answers. - Oct 10th 2012, 09:53 AMPlatoRe: counting problem
- Oct 10th 2012, 09:56 AMswordfish774Re: counting problem
okay, so can you please clarify the question? is the question about product of the factors? if yes then how do you go about it?

because 25*8= 5*40

this will lead to double counting..