Porch Potatoes

Aug 19, 2017

RAY: Potatoes are 99 percent water and one percent what? Potato. So say you take a bunch of potatoes, like 100 pounds of potatoes and you set them out on your back porch to dry out.

TOM: Yeah, when they are dry they should weigh about a pound.

RAY: Well, we’re not drying out completely. And as the potatoes dry out the water begins to evaporate. And after a while, enough water has evaporated so that they are now 98 percent water. If you were to weigh those potatoes at that moment...

TOM: They'd be lighter.

RAY: Yes, how much lighter? That's the question. Now you can solve this puzzler algebraically, and if you don't solve it algebraically, you are going to get the wrong answer.

TOM: Really?

RAY: Really.What's your answer, off the top of your head?

TOM: 99 pounds.

RAY: You are wrong.



RAY: Now, unencumbered by the thought process as usual, my brother guessed 99 pounds.

TOM: Yeah.

RAY: Now, when I guessed, off the top of my head, I guessed about 90 pounds.

TOM: 'Cause it just feels right.

RAY: But if you do the math, 1 percent of 100 --which is what the potato is-- is one pound. As we told you, that's 1 percent. So 2 percent, when it’s 98 percent water, two percent of the new weight of the mass is still going to be equal to that one pound, and 2 percent of 50 pounds is a pound. So the potato weight is now 50 pounds, not 100.

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