Mathematics
20 Online
OpenStudy (diamondanon2):
In how many ways can 5 boys and 5 girls be seated at a round table so that the boys and girls are seated alternately?
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OpenStudy (diamondanon2):
Answer choices are
14,400
2,880
576
OpenStudy (diamondanon2):
@ShadowLegendX
ganeshie8 (ganeshie8):
Let's first put the boys in a circle.
ganeshie8 (ganeshie8):
How many ways can you arrange 5 boys in a circle ?
OpenStudy (diamondanon2):
25
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ganeshie8 (ganeshie8):
Nope, try again.
OpenStudy (diamondanon2):
oops sorry how about 120
ganeshie8 (ganeshie8):
try again
OpenStudy (diamondanon2):
um what do I multiply then?
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OpenStudy (diamondanon2):
it cant be 5 times 5
ganeshie8 (ganeshie8):
How good are you at permutations and combinations ?
OpenStudy (diamondanon2):
eh
OpenStudy (diamondanon2):
new to it
OpenStudy (diamondanon2):
I know the whole
n
----r ! parts
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ganeshie8 (ganeshie8):
Okay, good. Let me ask you a question.
OpenStudy (diamondanon2):
and no I cant marry you sorry
OpenStudy (diamondanon2):
that was a joke
ganeshie8 (ganeshie8):
Suppose you went to a restaurant and want to have breakfast with coffee.
There are 5 kinds of items to choose for breakfast,
and 4 kinds for coffee.
OpenStudy (diamondanon2):
okay
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ganeshie8 (ganeshie8):
Haha that's funny! So my question is how many different ways are there to have breakfast with coffee ?
OpenStudy (diamondanon2):
the answer to that would be 5
OpenStudy (diamondanon2):
oh sorry would it be 20
OpenStudy (diamondanon2):
:P nope thats wrong too
OpenStudy (diamondanon2):
120
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ganeshie8 (ganeshie8):
5 ways to choose breakfast.
After you pick an item for breakfast, there are 4 choices for coffee.
ganeshie8 (ganeshie8):
Notice that for each type of breakfast, there are 4 choices for coffee.
OpenStudy (diamondanon2):
naw so it would be 20
ganeshie8 (ganeshie8):
Yes! you see how it works right ?
ganeshie8 (ganeshie8):
Let's get back to our original problem
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ganeshie8 (ganeshie8):
How to arrange 5 boys in a circle
OpenStudy (diamondanon2):
|dw:1471327916046:dw|
ganeshie8 (ganeshie8):
Excellent! that is a nice way to visualize above problem
OpenStudy (diamondanon2):
would it be 125 then?
ganeshie8 (ganeshie8):
Let's first arrange them in a straight line :
|dw:1471328079922:dw|
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OpenStudy (diamondanon2):
okay
ganeshie8 (ganeshie8):
For the first position, you can choose any one from the available 5 boys. So there are 5 ways for the first position :
|dw:1471328134574:dw|