How many ways are there to select 6 students from a class of 25 to serve on a committee?

25 ways to select the first one, 24 ways to select the second one, ... 20 ways to select the last one. Those same 6 can be selected in 6! different orders, so there are really 25·24·23·22·21·20/6! = 177,100 ways to select the students without regard to order.