[bigpooch]

Not quite, but you are on the right track.

Out of the integers between 7 and n, 1/2 are not divisible
by 2, (1/2)(2/3) = 1/3 are not divisible by 2 or 3, and
(1/2)(2/3)(4/5) = 4/15 are not divisible by 2, 3 or 5.

That's not quite the ratio desired, but the answer should
now be obvious.