shoonya wrote:

bkk145 wrote:

6. How many different five-letter combinations can be created from the word TWIST?

A. 5

B. 24

C. 60

D. 120

E. 720

I got 42 which is not among the answer choices.

This is how I solved it:

TWIST

if both T's are together, the number of ways = 4! = 24

when both T's are spaced they either are

TXTXX

or

TXXTX

or

TXXXT

in all three such cases, the total number of words = 3*3! = 18

total number of 5 letter words = 24+18 = 42.

Guys, I think I got it. I missed a few calculations in my last post.

when both T's together, the total number of ways = 4! = 24

when they are apart, they are

apart by one space :

TXTXX

XTXTX

XXTXT

total number of ways = 3*3! = 18

apart by two spaces :

TXXTX

XTXXT

total number of ways = 2*3! = 12

apart by three spaces

TXXXT

total number of ways = 3! = 6

total number of ways = 24+18+12+6 = 60.

how is the formula M!/L! is derived though?

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