Problem: the present population of a town is 4320 . population increase rate is 20 % p . a . find the population of town before 2 years ?
Rationale: "p = 4320 r = 20 % required population of town = p / ( 1 + r / 100 ) ^ t = 4320 / ( 1 + 20 / 100 ) ^ 2 = 4320 / ( 6 / 5 ) ^ 2 = 3000 ( approximately ) answer is d"
annotated_formula: add(4320, divide(multiply(4320, 20), const_100))