Problem: john purchased some shirts and trousers for $ 1550 . he paid $ 250 less for the shirts than he did for the trousers . if he bought 5 shirts and the cost of a shirt is $ 20 less than that of a trouser , how many trousers did he buy ?
Rationale: "given that the total purchase of two items cost 1550 . so the average purchase of one item will cost 1550 / 2 = 775 . its given as total shirt cost 250 $ less . hence total shirt cost = 775 - 125 and total trouser cost = 775 + 125 5 shirts = 650 $ = = > one shirt = 130 $ one trouser = 130 + 20 = 150 $ total trousers = 900 / 150 = 6 . c"
annotated_formula: divide(subtract(1550, multiply(5, add(20, 20))), add(add(20, 20), 20))