Define N as the random variable that marks the number of plane crashes in a certain month. We are going to use Poisson ~imation since we are given that the average number of crashes is 2.2. Now, we have that N pois a) P(N>2)=1-P(N=0)-P(N=1)-P(N=2) =1-e^(-2.2)-2.2e^(-2.2)- (2.2^2)/(2!)e^(-2.2) ~0.3773 b) Since the average number of crashes in one month is 2.2, the average number of crashes in two months is 4.4. Hence, if we say that N_1 is the number of crashes in two months, we have that N_1 pois. Thus P(N_1>4)=1-P(N_1=0)-P(N_1=1)-P(N_1=2)-P(N_1=3)-P(N_1=4) =1- sum_(k=0)^4 (4.4^k)/(k!)e^(-4.4)~0.44882 c) If we say that N_2 marks the number of crashes in next three months, using the same argument as in a) have that N_2. Hence P(N_2>5)=1- sum_(k=0)^5 (6.6^k)/(k!)e^(-6.6) ~0.64533