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Counting methods

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Counting methods

by alsergi » Thu Aug 21, 2008 7:42 am
Hi! could anyone help me with this?

How many even numbers, larger than 400, with 3 digits, can be formed using the digits 1,2,3,4,5,6,7,8?

a. 160
b. 620
c. 640
d. 2048
e. 2520

Thank you very much!!
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Re: Counting methods

by sudhir3127 » Thu Aug 21, 2008 7:57 am
alsergi wrote:Hi! could anyone help me with this?

How many even numbers, larger than 400, with 3 digits, can be formed using the digits 1,2,3,4,5,6,7,8?

a. 160
b. 620
c. 640
d. 2048
e. 2520

Thank you very much!!
IMO A .160
do let me know if its right so that i can post my solution..
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by pepeprepa » Thu Aug 21, 2008 8:03 am
My way:

_ _ _

For the first one you can chose among: 4,5,6,7,8 -->5 ways
For the second one you can chose among: 1,2,3,4,5,6,7,8 -->8 ways
For the third one (you want it even) you can chose among: 2,4,6,8 -->4 ways

You mutliply all possibilities: 5*8*4=160

so A
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