Start the problem by first finding out how many 1/4 cups of water equal 1 full cup of water.

, therefore we can see that every 1 cup of water is equivalent to 4 1/4 cups of water. Now we will find the total number of cups of water Greg drank on monday and tuesday by adding 5 + 4 = 9. Multiply this number by 4 and you have the total number of 1/4 cups of water Greg drank on Monday and Tuesday combined.