I am sorry to come back to this question, and while the solution now seems nice, I wouldn't have thought of this approach during an exam.. I would have thought of probabilities approach or something... is there any other formal approach?
You get 1 out of 5 colors every time, and while it may be very slim, but there is a chance, you'll pull them all out of the same color, while there is no "70" option in the answers, am I missing something? what's wrong in my train of thought? would love to hear back...