the population of a town is 8100 . it decreases annually at the rate of 10 % p . a . what was its population 2 years ago ?
"formula : ( after = 100 denominator ago = 100 numerator ) 8100 × 100 / 90 × 100 / 90 = 10000 e )"
subtract(subtract(8100, multiply(8100, divide(10, const_100))), multiply(subtract(8100, multiply(8100, divide(10, const_100))), divide(10, const_100)))