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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?

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

ganeshie8 (ganeshie8):

Nope, try again.

OpenStudy (diamondanon2):

oops sorry how about 120

ganeshie8 (ganeshie8):

try again

OpenStudy (diamondanon2):

um what do I multiply then?

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

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

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

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

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|

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|

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