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of 10

Fast Counting (The Counting Principle)

26 * 25 * 10 __ __ __ __ __

Now the numbers... no restrictions yet.
 

Suppose the first number is a 6:

26 * 25 6 __ __ __ __ __
Now, this guy can't be a 6...
9 possibilities


26 * 25 * 10 * 9 __ __ __ __
 

Suppose these are the first two numbers:

26 * 25 6 4 __ __ __ __
This guy can't be a 4...  But, it CAN be a 6
9 possibilities again!
 

26 * 25 * 10 * 9 * 9 __ __ __
 

Can you figure out the rest?

26 * 25 * 10 * 9 * 9 __ __ __ = _______

 

TRY IT:

How many CA license plates are there if no two adjacent numbers or letters can be the same?