50 pounds.

100 lb of potatoes with 99% water weight means there’s 99 lb of water and 1 lb of solids, a 1:99 ratio.

If the water decreases to 98%, then the solids account for 2% of the weight. The 2:98 ratio reduces to 1:49. Since the solids still weigh 1 lb, the water must weigh 49 lb for a total of 50 lbs for the answer.

Read more at the Potato Paradox wikipedia page.

29%

To read more about this, see the False Positive Paradox page on Wikipedia.

Paula had $48 and Quincy had $12.

If Q is the amount Quincy had, then 3(4Q – 33) = Q + 33

Solved, Q = 12.

It turns out they all save the same amount of fuel.

If you travel 100 miles:

100 / 10 = 10 gallons used
100 / 12 = 8 1/3 gallons used

10 – 8 1/3 = 1 2/3 gallons saved

100 / 30 = 3 1/3 gallons used
100 / 60 = 1 2/3 gallons used

3 1/3 – 1 2/3 = 1 2/3 gallons saved

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Technically, the answer is infinity. If you keep going halfway, you’ll never actually make it to the doorway.

But in practice, after 10 steps you’ll be 1/8th of an inch to the doorway and anyone behind you would say to stop being a baby and take a real step through the doorway already.