Posted by jake on Sunday, November 4, 2007 at 12:27pm.
In the first case, you are free to choose only the first and lat digits. The first digit must start with 1 and there are 9 of them. The last digit can start with any number 0 to 9, and there are 10 of them. That makes the number of possibilities 9x10 = 90
Try your own hand at the second one. There are a lot of similarities with the first.
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