How many seating charts can a teacher arrange for 20 students if there are 25 desks?

Question

You want to visit 15 beaches, but only have time to visit 4. In how mant ways can you choose a group of 4 out of those 15?

Thanks a lot

Answer 1

The way to figure these questions out is actually very easy...or not.

You will be dealing with factorials.  The factorial for 4 is

4 *3*2*1=24

So to answer your question for the beaches...you would say:

15 factorial divided by 11 factorial...11 factorial since 15 choices - 4 possibilities is 11.

The answer is 32,760.

For the desks you would do 25 factorial divided by 5 factorial because 25 choices - 20 possibilites is 5.

The fist part of the answer is 129260...

See if you can figure it out.

Good Luck!