How many combinations of license plates are there, if the license plate consists of 3 letters and 3 numbers where there is no specific order of which letter or number comes first. Repetition of letter/number is allowed. Example: AAA123 is one license plate A1A2A3 is another license plate

26)(26)(26)(10)(10)(10)=17576000

How many different committees of 3 people can be chosen to work on a special project from a group of 7 people?

this is a counting problem called a choose problem: 7 choose 3 (a combination). 

7 choose 3 =