To find the decrease in the percentage of students from the previous year to the current year, you must establish a baseline to be your maximum (100%). For this we'll use the 92 students. From here, we need the current 63 students to establish the current percentage.
Simply:
63/92 == .6848 == 68.48%
So our current percentage of students is 68.48%. We want the decrease of the students compared to the previous percentage so we'll need to do the maximum minus the current to get the change (or the decrease).
100% - 68.48% = 31.52%
Thus, the population increase (decrease) for this year is 31.52%.
