wufabif wrote:

Hey chetan2u!

Thank you for your fast response to my question.

Combinations are (hopefully not any longer) a great weakness of mine, so i do not yet understand how you derived the equations used for the possibilities.

Is there any link to a guide or forum post which i can use to refresh my combinations formulas from highschool in order to be able to reproduce your calculations?

Best regards

Hi,

i'll just explain how this equation has come..

EXCESS has 6 places...

the first place can be filled by any of the 6, next by remaining 5, and so on till you are left with only one place and one letter..

so ways=6*5*4..*1=6!..

but these 6! has duplication of Es and Ss..

example if you are taking 6 position as first E and 4 position for second E...

this will be same when you are taking 4 position as first E and 6th position for second E...

that is why we divide the answer by 2!, as these 2 places within two Es can be done in 2! ways..

so ways become 6!/2!2!..

Do practice these somes by putting combinations in the search tag..

and you will find theory too ..

_________________

1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372

2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html

GMAT online Tutor