License plates consist of 3 letters, followed by 4 numbers (0 to 9), with repetition allowed.
a) how many license plates do not contain the sequence DOG?
+36915 DOG can only occupy one position in the leter group as there are only three letters allowed
4 numbers would be 10 000 possibilities (0000 - 9999)
soooo 26 x 26 x 26 x 10 000 - 10000
