# counting problem

• Oct 10th 2012, 08:51 AM
swordfish774
counting 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 AM
Plato
Re: counting problem
Quote:

Originally Posted by swordfish774
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

This is not a homework service. Please show what you have done.
• Oct 10th 2012, 09:37 AM
swordfish774
Re: 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 AM
Plato
Re: counting problem
Quote:

Originally Posted by swordfish774
why do you say 'this is not a homework service'? i use it to solve doubts and verify answers.

When someone simply posts a list of problems with no comments, we assume that the person expects to get the answers just given to them.
• Oct 10th 2012, 09:56 AM
swordfish774
Re: 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..