Hello there,
The last rank admitted in the college is the cut-off rank for that year for that particular college. College predictions are done based on this cut-off rank, using the previous year data. The cut-off rank changes every year depending on the difficulty of the paper, and the number of candidates appearing for it. So there is no fixed cut-off percentile or rank. It keeps on varying every year.
Hope this answer helps you.
Thank you!!