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krishrads
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There are 12 girls and 15 boys in a class.In how many ways 02 Jun 2005, 10:56
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There are 12 girls and 15 boys in a class.In how many ways can we form 4 pairs for a dance?

Thanks



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There are 12 girls and 15 boys in a class.In how many ways 02 Jun 2005, 11:37
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If only a girl and a guy can pair up for a dance, then
12x15 + 11x14 + 10x13 + 9x12 = 180 + 154 + 130 + 108 = 572
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sparky
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There are 12 girls and 15 boys in a class.In how many ways 02 Jun 2005, 13:35
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krishrads
There are 12 girls and 15 boys in a class.In how many ways can we form 4 pairs for a dance?

Thanks
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let's see

(12c4)(15c4)*4!
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emilem
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There are 12 girls and 15 boys in a class.In how many ways 02 Jun 2005, 14:30
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sparky
krishrads
There are 12 girls and 15 boys in a class.In how many ways can we form 4 pairs for a dance?

Thanks

let's see

(12c4)(15c4)*4!
Show more


sparky, why to multiply with 4!? Isn't it just (12C4)*(15C4)
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sparky
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There are 12 girls and 15 boys in a class.In how many ways 02 Jun 2005, 14:36
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emilem
sparky
krishrads
There are 12 girls and 15 boys in a class.In how many ways can we form 4 pairs for a dance?

Thanks

let's see

(12c4)(15c4)*4!

sparky, why to multiply with 4!? Isn't it just (12C4)*(15C4)
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emilem, i am not sure it's correct but the idea is you first pick 4 boys and 4 girls, not ordered. Then you line up, say, all the girls in any particular order and start arranging the boys and matching them with preordered girls - so 4! for boys.
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There are 12 girls and 15 boys in a class.In how many ways 02 Jun 2005, 14:46
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emilem
sparky
krishrads
There are 12 girls and 15 boys in a class.In how many ways can we form 4 pairs for a dance?

Thanks

let's see

(12c4)(15c4)*4!

sparky, why to multiply with 4!? Isn't it just (12C4)*(15C4)
Show more


you multiply by 4! to count the different ways to arrange the pairs. it is (12C4)*(15C4) to count the ways to choose the boys/girls from their respective groups. we have 4 spaces for 4 pairs. 1st space is 4 ways, 2nd space is 3 ways and so on...
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There are 12 girls and 15 boys in a class.In how many ways 02 Jun 2005, 19:52
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kapslock
If only a girl and a guy can pair up for a dance, then
12x15 + 11x14 + 10x13 + 9x12 = 180 + 154 + 130 + 108 = 572
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Good solution kaps !

HMTG.
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HongHu
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There are 12 girls and 15 boys in a class.In how many ways 02 Jun 2005, 22:19
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HowManyToGo
kapslock
If only a girl and a guy can pair up for a dance, then
12x15 + 11x14 + 10x13 + 9x12 = 180 + 154 + 130 + 108 = 572

Good solution kaps !

HMTG.
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Don't think this is correct though.



Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
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Thank you for understanding, and happy exploring!