Rachel drinks 2 glasses of water on Sunday and 4 glasses of water on Monday. Then she drinks 3 glasses of water every day for the next 4 days. One glass of water is 10 ounces of water. If Rachel wants to drink a total of 220 ounces of water in the week (Sunday to Saturday), how many glasses of water should she drink on Saturday? Let's be accurate as possible.
From Sunday and Monday, Rachel drinks 2 + 4 = 6 glasses of water. From Tuesday to Friday, Rachel drinks 3 * 4 = 12 glasses of water. The total glasses of water she drinks from Sunday to Friday is 6 + 12 = 18 glasses of water. The total ounces of water she drinks from Sunday to Friday is 18 * 10 = 180 ounces. The ounces of water she should drink on Saturday is 220 - 180 = 40 ounces. The glasses of water she should drink on Saturday is 40 / 10 = 4 glasses of water.
The answer: 4.