An airline has determined that 4% of people do not show up for their flights. To avoid having empty seats, the flight is overbooked. A large jet holds 300 people. What is the probability that some travelers will not get a seat if 310 tickets are sold?

I know that the expected number would be 310 times 0.04 and i calculated the standard deviation, but it gave me the the wrong z-score. Could someone help please?

Answer is 0.204