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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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kapslock
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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.



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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!