A team of 8 members are going to plan an excursion tour.the were going to plan in 2 cars.one car can sit 5 members and another car can sit 4 members.how many ways they can be sit together?

8C5 + 8C4

the reason is that once you have chosen the 4 or 5 people for the larger car, the rest go into the smaller car.

Note that you could choose the smaller car first, getting 8C3+8C4 ways, but that's the same, since 8C5 = 8C3