COLD OPEN+ · MATH
COLD OPEN+ · Nº 13 of 40
How Drying Potatoes 'Lost' Half Their Weight
100 pounds of potatoes are 99% water. Dry them slightly to 98% water and they weigh 50 pounds. It feels like a trick. The math is exact.
Wikimedia Commons · Hans Braxmeier · CC0
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THE SETUP
99%
OF 100 LB OF POTATOES IS WATER
Start with 100 pounds
You have 100 pounds of potatoes. They're 99% water by weight. That means 99 pounds of water and just 1 pound of actual potato solids.
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THE CHANGE
Let them dry to 98% water
You leave them out. A little water evaporates. Now they're 98% water instead of 99%. That's a tiny change — one percentage point. How much could they possibly weigh now?
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THE ANSWER
50 pounds.
They now weigh half of what they did. Losing a single percentage point of water dropped 100 pounds to 50. It feels like a math error. It isn't.
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THE LOGIC
Follow the solid part, not the water
The trick is to track the thing that doesn't change.
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Potato solids never evaporate: always 1 pound
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At 99% water, that 1 lb of solids = 1% of the total
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At 98% water, the solids are now 2% of the total
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If 1 lb = 2% of the total, the total is 50 lb
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The weight halved because the solids' share doubled
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WHY YOUR BRAIN BALKS
Small percentage, huge effect
The intuition trap is the percentage.
FEELS LIKE
'1% change = tiny change'
REALLY IS
The solids' share doubled (1% → 2%)
THE ANCHOR
Watch the constant, not the percent
THE LESSON
Percentages hide the real quantities
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THE POINT
A tiny move in a percentage can be an enormous move in reality.
Percentages feel intuitive and lie constantly. When a number surprises you, find the thing underneath that isn't changing.
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THE RECEIPTS · TRY IT YOURSELF
You can check every step
A classic 'veridical paradox' — surprising but provably true.
NAME
The Potato Paradox
TYPE
A classic recreational-math puzzle
THE SETUP
100 lb of potatoes, 99% water
THE MOVE
Dry them to 98% water
THE RESULT
Weight drops to 50 lb
WHY
The 1 lb of solids goes from 1% to 2% of the whole
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DISCUSS
What do you think?
Where do misleading percentages show up in news, ads, or sports stats?
What's the fixed 'potato solid' hiding inside a confusing percentage you've seen?
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