Quant. Reason. question, anyone please?

[Uracil]

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It should be easy, but I just don't seem to get it. Could anyone please explain?

How many two letter arrangements exist from the letters: A, B, C, D, and E?
No letter may be used more than once in each arrangement.

Answer: 20 arrangements

Thank you.

 

[GRAD]

I hate probabilty- but its like this, because its not random, you have to do this permutation:

5!
----
3!

which is # of total things/ # of total things - how many you take at a time

the equation is
n!/n-r!

Its confusing, try to go on the web and figure them out cause they get way harder....

 

[Uracil]

perfect. Thank you. 😉 😀

GRAD..You'll ace the DAT!! Exito!

 

[abzirian]

Nothing on the QR of the DAT requires any real probability equations as long as you can use some creativity. As for your question, you can simply think out the combinations. A can combine with B, C, D or E so that's 4 combinations. B with C, D, or E which is 3, and so on. 4+3+2+1 = 10. Each combination can be switched (so AB and BA are separate combinations, which we didn't account for in the 10) s 10x2 - 20.