Pump B alone fills a tank in 9 hours. Pump C takes 15 hours to fill the same tank alone. If pumps A, B and C are used, the tank fills in 5 hours. How long does it take pump A to fill the the tank alone?

You’re ordering more thread for blue jeans co. you usually purchase from ted’s threads, which sells 12 thread spools for $27. you recently received a notice from wade's wares that says you can buy thread from them for $2.30 each for the first 2 dozen and $2 a spool thereafter. you need to order 5 dozen spools. what percentage can you save by going with wade’s wares?