Math problem

[myair]

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Jill has 6 different books.She will select one book Monday and a different one on Wednesday. In how many ways can Jill select 2 different books?

answer is 30 I think 5x6

but why or how come they chose this?😕

 

[visbimmer79]

Jill has 6 different books.She will select one book Monday and a different one on Wednesday. In how many ways can Jill select 2 different books?

answer is 30 I think 5x6

but why or how come they chose this?😕

Hint) Choosing "a" on Monday and "b" on Wednesday

and

Choosing "b" on Monday and "a" on Wednesday

is different! (Count as different event!)

Hint II) Always it's better to study case by case for statistics always "before" the test!

Hint III) If they asked how many different sets are possible, it becomes a totally different story.

12 23 34 45 56
13 24 35 46
14 25 36
15 26
16

Now, who else can explain this in terms of nCr or nPr?

Hint) Is Order important?

 

[myair]

thank you,

I just figured it is a combination question u can do by n!/n-k!

how you did it is another way as well 🙂

 

[visbimmer79]

thank you,

I just figured it is a combination question u can do by n!/n-k!

how you did it is another way as well 🙂

6!/(6-2)! 2! for the second one. Cuz it's just choosing 2 out of 6 things without concerning about the order of ur choice. 6C2

And all kinds of variation starts from here.

Your original answer should be 6P2

Am I remembering right? 😛

 

[myair]

yes but we have to use this formula

b/c the answer is 30 not 15.
that'a why I was confused I was thinking it must be 15 too.

 

[klutzy1987]

However since there are 2 different ways that the outcome can happen. A-Monday, B-Wednesday
B-Monday, A-Wednesday

Therefore you have to multiply 6c2 by 2 so 15*2=30

 

[myair]

thank you I got it now 🙂