Make 100 with four 9s

The classic four nines puzzle: build an expression from exactly four 9s that equals 100. 100 cannot be made with + - × ÷ alone (the solver checked every expression) — you will need to stick 9s together (like 99) or use decimals (like .9).

Solutions using only + - × ÷

No expression made of four plain 9s and + - × ÷ reaches 100 — the solver checked every possible expression.

Solutions with concatenation and decimals

9 / 9 + 99 = 100
99 / .99 = 100
.9 / .9 + 99 = 100
(99 - 9) / .9 = 100
9 × 9 / .9 / .9 = 100

…and 9 more at this tier.

Solutions with square roots, factorials, exponents

9! / 9! + 99 = 100
(9 - 9)! + 99 = 100
(.9 - .9)! + 99 = 100
(9! - 9!)! + 99 = 100
99 + sqrt(9) / sqrt(9) = 100

…and 14 more at this tier.

33 distinct solutions found in total, after removing trivial rearrangements.

Make 99 with four 9s

The Number Lab

Same idea, different constraints: four 9s, four 4s, or any four digits you like.

Four Nines — the daily puzzle
Four Nines solver — every target, solved
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Four Fours solver — including the impossible five
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Today's 24 — one new hand a day

Play the daily Four Nines puzzle, pick another number in the solver, or find more free math games.