A sign on the petrol pumps of a chain of petrol stations encourages customers to have their oil checked, claiming that one out of every four cars should have its oil topped up. Assuming this claim is true:
(b) What is the probability that at least half of the next 10 cars entering a petrol station should have their oil topped up? At least half of the next 20 cars?
(c) What is the probability that at least 5 but not more than 8 of the next 20 cars will need their oil topped up?
(d) What is the mean and standard deviation of the number of cars out of the next 20 that will need their oil topped up?