Question

Need some help on these last two questions on my notes sheet.

http://i.imgur.com/EFySycch.jpg

Answer 1

after 5th day means first 5 days it did not hit. Let P(A) represent the probability it will hit the sidewalk of day A, A = 1..n

If the total probability of all events for n days is 1, then we can subtract the probability it hits on days 1 thru 5. i.e. P(1). P(2)...P(5) from 1 to find by complementary probability.
1 - [P(1)+...+P(5)]

Last question: P(3) + P(4) + P(5)