combination question ?!?

im stuck on this question, and i need some help understanding what to do:

an area code is made up of three digits;

the first digit of an area code cannot be 0 or 1, and the third digit cannot be 1 when the second digit is 1. how many different area codes are possible in this system?

thanks in advance!

Top 1 Answers

A few days ago

Anonymous

Favorite Answer

First forget about having to not end in “1 1”

If the first digit can’t be 0 or 1, there are

8 x 10 x 10 = 800 arrangements

Now, we have to subtract the number of arrangements that end in “1 1”. That would be 8 ways (211, 311, 411, etc)

So the answer is 800 – 8 = 792

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