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help with permutation problem!

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help with permutation problem!

by ashish1354 » Tue Feb 17, 2009 10:54 pm
28. How many four-digit numbers that do not contain the digits 3 [color=red]or[/color] 6 are there?

28. How many four-digit numbers that do not contain the digits 3 [color=green]and[/color] 6 are there?

can someone explain the difference between the two questions?
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sorrry guys !

by ashish1354 » Tue Feb 17, 2009 11:05 pm
Can someone please explain the difference between the following two problems?

How many four-digit numbers that do not contain the digits 3 or 6 are there?

and

How many four-digit numbers that do not contain the digits 3 and 6 are there?
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Re: sorrry guys !

by billzhao » Tue Feb 17, 2009 11:37 pm
ashish1354 wrote:Can someone please explain the difference between the following two problems?

How many four-digit numbers that do not contain the digits 3 or 6 are there?

and

How many four-digit numbers that do not contain the digits 3 and 6 are there?

The number of 4-digit integers that do not contain 3 is 8*9^3
The number of 4-digit integers that do not contain 6 is 8*9^3
The number of 4-digit integers that do not contain 3 and 6 is 7*8^3


So The number of 4-digit integers that do not contain 3 and 6 is 7*8^3
The number of 4-digit integers that do not contain 3 or 6 is 8*9^3+8*9^3-7*8^3
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by mjjking » Wed Feb 18, 2009 2:13 am
Could you please explain why billzhao?
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by billzhao » Wed Feb 18, 2009 5:57 am
mjjking, I guess i need to explain the relationship of the three sets. I have drawn the graph for explanation.
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by naaga » Wed Feb 18, 2009 6:16 am
The number of 4-digit integers that do not contain 3 is 8*9^3
The number of 4-digit integers that do not contain 6 is 8*9^3
The number of 4-digit integers that do not contain 3 and 6 is 7*8^3


Billzhao , why did you take 8*9^3 actually it is 9 * 9 * 9 * 9

plz don't misunderstand me I am bit weak in this area

so, kindly make for me.....thankyou
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by billzhao » Fri Feb 20, 2009 5:00 am
naaga wrote:The number of 4-digit integers that do not contain 3 is 8*9^3
The number of 4-digit integers that do not contain 6 is 8*9^3
The number of 4-digit integers that do not contain 3 and 6 is 7*8^3


Billzhao , why did you take 8*9^3 actually it is 9 * 9 * 9 * 9

plz don't misunderstand me I am bit weak in this area

so, kindly make for me.....thankyou
Because the first digit cannot be "0"
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