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.