My son drinks 3 cups of milk a day. There are 8 ounces in a cup. How many ounces would he have drunk after 10 weeks?

 Question: My son drinks 3 cups of milk a day. There are 8 ounces in a cup. How many ounces would he have drunk after 10 weeks? 

Solution: He drinks 3 cups of milk in a day. so he will drink:
3 x 7 = 21 cups in a week and so he will drink:
21 x 10 = 210 cups in 10 weeks.

Now it is given that there are 8 ounces in a cup. So, after 10 weeks he would have drunk 8 x 210 = 1689 ounces.