The Sprite question took me a lot of thought. Maybe 3 minutes. Here's how I did it:
First, I realized that on the 20th day, he would have drinken the entire contents of the bottle, so it is on the 20th day where he runs out of Sprite.
Next, you find the amount of TOTAL LIQUID he drinks in those 20 days. It is:
20
E (k)
k=1
Or, the sum of all integers between 1 and 20. that is: 1+20 + 2+19 + 3+18 ... + 10+11. This is 21*10, or 210 total ounces of fluid.
Now, the amount of Sprite never changes. Therefore, of that 210 ounces of fluid, 20 ounces of it was Sprite, and the rest was water. Therefore, the amount of WATER is:
210-20=190 ounces of water. A tricky problem, yes.
And I took the quiz again yesterday with the same answers, but in under 6 minutes, and my IQ became 204. So the time you take does play some factor in your scoring. (The extra 23-24 minutes lowered the score 13 points.)
Congratulations! You have just been blessed by the wisdom of Steve.