Tackle wild 'how many?' questions by breaking each into factors you can guess, then multiply them into a single back-of-the-envelope estimate.
Each question is a Fermi estimation puzzle, a quantity too big to know exactly. Enter a guess for each contributing factor and the game chains them into your total estimate. You're scored on how close you land measured in orders of magnitude, not exact digits. Optionally wager a question to double your points if you finish within 10x, or zero it if you miss.
Back of Envelope is an estimation game built on Fermi problems and order-of-magnitude reasoning.
Estimating a quantity too large to know by chaining guesses about its factors is the Fermi problem, the order-of-magnitude estimate named for Enrico Fermi.
Entering each contributing factor separately, and letting the game chain them, is the original structure.
Decomposition is the entire method. Individual factors are each wrong, but their errors are independent and partly cancel, so a chain of rough guesses lands far closer than one bold guess at the answer — which is why the technique survives despite every step being admittedly approximate.
Back of Envelope is an estimation game built on Fermi problems and order-of-magnitude reasoning. It's an original free browser game built for PlayPendium.