In a certain region all license plates are composed of three letters followed by three numbers, or three numbers followed by three letters. Find how many license plates are possible.
There are many ways to fill the license plate in. To demonstrate it, we create a template:
_ _ _ _ _ _ = 26 * 26 * 26 * 10 * 10 * 10
There are $26^3$ ways to choose the letters and $10^3$ ways to choose the numbers. Thus, the number of license plates are $26^3 \cdot 10^3= 17576000.$