A study of the weekly car sales from last year resulted in the following information. Only once did the dealership sell no cars in a week. Three times they sold only 1 car, five times they sold 2 cars, eight times they sold 3 cars, they never sold 4 cars, eleven times they sold 5 cars, twenty times they sold 6 cars, they never sold 7 cars, three times they sold 8 cars and one time they sold 9 cars. Find the probability that at most 4 cars were sold in a week.