If the letters of the word 'FAST' are arranged as in dictionary, find the rank of FAST.

Dear Student,

Let's arrange letters of the word 'FAST' in alphabetical order - AFST
Now fix A at first place
A _ _ _
Now, by arranging the remaining 3 letters in the blank space, we get = 3! (factorial of 3) = 6 words
Now, Lets fix F,
F _ _ _ 
Now the first word formed in dictionary when F is fixed at first place will be FAST
Therefore, FAST is the 7th word in the dictionary.
Therefore, rank of FAST is 7th

Regards,