Question

An integer is chosen at random from the first 40 positive integers. What is the probability that the integer chosen is divisible by 6 or 8?

Answer 1

im thinking 11/40 but i read somewhere else its 9/40. Could you please explain how you get your answer

Answer 2

how many of the 1st 40 integers are divisible by 6?
how many by 8?
how many by both?

Answer 3

P(A or B) = P(A) + P(B) - P(A and B)

Answer 4

6 are divisible by 6.
5 are divisible by 8
correct?

Answer 5

yes and how many are divisible by both 6 and 8?

Answer 6

umm. is there an easy way to find out?

Answer 7

every 4th multiple of 6 should also be divible by 8

or (to think of it in a different way) every 3rd multiple of 8 should be divisible by 6.


why?

6*4k = 2*4*3k = 8*3k => multiple of 8

8*3k = 4*2*3k = 6*4k => multiple of 6

Answer 8

so only one is divisible by 6 and 8.

Answer 9

so the answer would be 10/40 or 1/4.... correct?

Answer 10

yep! good job!

Answer 11

ok thanks! Im going to ask another that is more complicated. if you could help i would appreciate it:)

Answer 12

just @ me in your post and i will help