when the price of an article was reduced by 20 % its sale increased by 80 % . what was the net effect on the sale ?
"if n items are sold for $ p each , revenue is $ np . if we reduce the price by 20 % , the new price is 0.8 p . if we increase the number sold by 80 % , the new number sold is 1.8 n . so the new revenue is ( 0.8 p ) ( 1.8 n ) = 1.44 np , which is 1.44 times the old revenue , so is 44 % greater . answer : a"
subtract(divide(multiply(add(80, const_100), subtract(const_100, 20)), const_100), const_100)