A shuttle service transports passengers from the airport to local hotels. The vans used have room for up to 6 passengers. Data collected over several years indicate that the number of passengers per trip to the hotels follow the following probabilities. Passengers: 1 2 3 4 5 6
Probability: 0.20 0.25 0.22 0.13 0.10 0.10

Required:
A van leaves the airport for the local hotels. What is the probability there are at least 4 passengers on board?