# quick question

• Nov 24th 2007, 07:01 PM
ihaveamathproblem
quick question
say a pin number is 5 digits long. The pin number must have one 2 in it anywhere in the pin. How many different combinations can there be?

I believe that there will be 16*10^4 but im not quite sure.

also another one, how many combinations can there be if the 5 digit pin number can only have even digits? I think 5^5, not so sure either though.

thanks.

and one i haven't quite thought about, an even number of even digits. zero even numbers count.
• Nov 25th 2007, 12:06 AM
CaptainBlack
Quote:

Originally Posted by ihaveamathproblem
say a pin number is 5 digits long. The pin number must have one 2 in it anywhere in the pin. How many different combinations can there be?

I believe that there will be 16*10^4 but im not quite sure.

The number containing no 2's is 9^5, the total number is 10^5 so the
number with at least one 2 is (10^5-9^5).

RonL
• Nov 25th 2007, 12:07 AM
CaptainBlack
Quote:

Originally Posted by ihaveamathproblem

also another one, how many combinations can there be if the 5 digit pin number can only have even digits? I think 5^5, not so sure either though.
th

There are 5 even digits 0, 2, 4, 6, 8. So the number of pins consisting only
of these digits is 5^5.

RonL
• Nov 26th 2007, 10:46 AM
ihaveamathproblem
thank you very much captain black.