Please make sure your handwritting is nice and clean. Also, try to make sure every detailed steps are clearly shown.

40. 1. The probability that a certain kind of cellphone will not get a cracked screen after it is dropped from a given height is 3 / 4. If we test 4 cellphones, nd the probability of obtaining (a) exactly 2 phones with good screens. (b) at least 2 phones with good screens. (c) at most 2 phones with good screens. 2. In a factory the probability of an accident on any given day is 0.002 and accidents are independent of each other. Assuming the Poisson approximation, nd the probability that in any given period of 1000 days (a) there will be an accident on one day. (b) there are at most three days with an accident