A swimming pool holds 600,000 liters of water. The pool has two drainage pipes. When the pool is completely full, the first pipe alone can empty it in 200 minutes, and the second pipe alone can empty it in 120 minutes. When both pipes are draining together, how long does it take them to empty the pool

Pls! does anybody know a shortcut for answering these types of questions in the future?

Giuseppi's pizza had orders for $931.00 of pizzas. the prices were $21 for a large pizza, 514 for a medium pizza, and $7 for a small pizza. the number of large pizzas was two less than four times the number of medium pizzas. thenumber of small pizzas was three more than three times the number of medium pizzas. how many of each size of pizza were ordered?

Acomputer store bought a program at a cost of $10 and sold it for $13. find the percent markup