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Permatution or Combination

 
 
Reply Sun 10 Apr, 2011 03:11 pm
we have 5 blue pens, 7 green pens, and 9 yellow pens How many different ways can we choose 2 of them if
a. The order is important
b. the order is not important

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Type: Question • Score: 0 • Views: 1,212 • Replies: 3
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engineer
 
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Reply Sun 10 Apr, 2011 04:02 pm
@daivinhtran,
a) 9: Three colors for the first pen, three for the second
b) 6: If blue is first, the second can be any of the three. If green is first and you've already counted blue, you have two options. For yellow, your only option is yellow.
daivinhtran
 
  1  
Reply Sun 10 Apr, 2011 04:27 pm
@engineer,
I think you were wrong
We choose it at the same time.

How about we choose 2 blue pens at the same times?
engineer
 
  2  
Reply Sun 10 Apr, 2011 05:53 pm
@daivinhtran,
It doesn't matter. Since you have so few options, you can just map them out yourself if you need to prove it.

Permutations
BB
BG
BY
GB
GG
GY
YB
YG
YY

For combinations just remove the ones that form duplicates (GB, YB, YG).
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