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**Wilmer** a = amount owing ; 1000

i = interest monthly ; .01

p = percentage payment ; .03

m = mimimum payment ; 15

Required is calculation of the month where the balance owing is such

that a switch to the minimum payment is required.

In other words, ap(1 + i - p)^n = m ; solving for n, and converting to integer:

n = INT{LOG[m / (ap)] / LOG(1 + i - p)} + 1

For above example, you'll get n = 35.

Actually, at month 35, ~493.07 is owing.

493.07 * .03 = 14.79 ; hence the switch to minimum payment of 15.