Today's Guess
One question a day. Don't look it up. Give a low and a high you are 90% sure the answer sits between, then see it worked out. Over time you'll see how often your ranges hold: about nine in ten is the goal.
Today
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Type two numbers, like 50 and 5,000.
Source: the published figure
How your ranges are doing
The last seven
Missed a day? They stay open. Pick one to try.
For children, the same idea lives in FermiForge on Spark & Anvil.