Casey is pumping water out of her well. She can pump 3 gallons a minute. She has 4 rows of 15 corn plants each, and each plant needs half a gallon of water. She also has 10 pigs, which each need 4 gallons of water, and 20 ducks that each need a quarter of a gallon of water. How many minutes does Casey need to spend pumping water? Let's answer step by step:
First find how many corn plants there are: 15 plants / row * 4 rows = 60 plants. Then find how many gallons of water of the corn needs: 60 plants * 1 / 2 gallon / plant = 30 gallons. Then find how many gallons of water the pigs need: 10 pigs * 4 gallons / pig = 40 gallons. Then find how many gallons of water the ducks need: 20 ducks * 1 / 4 gallon / duck = 5 gallons. Now add up all three quantities of water to find the total water needed: 5 gallons + 40 gallons + 30 gallons = 75 gallons. Now divide the total water needed by Casey's pumping rate to find how long she spends pumping: 75 gallons / 3 gallons / minute = 25 minutes. The answer: 25.