Short Interest Rules
To find the interest on a given sum for any number of days, at any rate
of interest, multiply the principal by the number of days and divide as
follows:
At 3 per cent, by 120 At 9 per cent, by 40
At 4 per cent, by 90 At 10 per cent, by 36
At 5 per cent, by 72 At 12 per cent, by 30
At 6 per cent, by 60 At 15 per cent, by 24
At 7 per cent, by 52 At 20 per cent, by 18
At 8 per cent, by 45