combinations

Question

just a refresher,

how many ways could you arrange the following letters? how do you approach these types agian? thanks
1)AABB

2)ABCDEF

3)AABBCC

4)AAB

ipc302 · Answer

to solve these kinds of problem first count the total no of alphabets say N and in the numerator put N! and if some of them are repeated r1 times , and some other r2 times ........divide the numerator by those factorial . so it becomes N!/(r1! *r2!)

ipc302 · Answer

you are always welcome .

gmatacer · Answer

a real refresher .. indeed!

willget800 · Answer

thanks a lot!

that was a good refresher!

ywilfred · Answer

1)AABB 
Number of ways to arrange any 4 letters = 4!
But A and B are repeated, so we need to consider that there are going to be duplicates. The total number of ways is therefore 4!/2!2! = 6 ways

2)ABCDEF 
The number of ways to arrange this is 6! simply because each letter is a different entity.

3)AABBCC 
The way to approach this is the same as explained in 1. It's 6!/2!2!2! = 90 ways.

4)AAB
Same as for 3. Number of ways = 3!/2! = 3

combinations

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