The total number of arrangement of the letters in the word ‘UNIVERSITY’ is 2!10!
(∵ Total letters = 10, I occurs twice)
Now, if 2I’s occurs together, then regard 2I’s as one letter.
Then, total number of arrangement in which 2I’s are not together =2!10!−9!
Hence, required prob =2!10!2!10!−9!=1−10!9!2!=1−51=54