The key to answering both questions is that we should understand that the probability of an event happening = 1 - the probability of the event not happening
Firstly, we want to calculate the probability of less than four
Probability of less than four = 1 - probability of four or more heads
that is 1 - 0.83 = 0.17
Probability of less than 8 = 1 - probability of 8 or more = 1-0.05 = 0.95
