Do you mean the probability of spelling “working” with 26 alphabetic tiles?
If so, then the probability of picking W first is 1/26. That leaves 25 tiles, so the probability of picking O next is 1/25, then R is 1/24 and so on.
Total probability of spelling WORKING is the product of all individual probabilities:
(1/26)(1/25)(1/24)(1/23)...(1/20)=1/3315312000=0.0000000003 approx.
The probability of spelling any particular 7-letter word is the same.
The probability of picking the letters of WORKING in any order is larger: (1×2×3×4×5×6×7)/(26×25×24×23×22×21×20)=1/657800=0.00000152 approx.