Make 79 with four 9s

The classic four nines puzzle: build an expression from exactly four 9s that equals 79. 79 cannot be made with + - × ÷, concatenation, or decimals (the solver checked every expression) — solutions need square roots, factorials, or exponents.

Solutions using only + - × ÷

No expression made of four plain 9s and + - × ÷ reaches 79 — the solver checked every possible expression.

Solutions with concatenation and decimals

Concatenation and decimals do not help for 79 either — every combination was checked.

Solutions with square roots, factorials, exponents

sqrt(9)!! / 9 - 9 / 9 = 79
sqrt(9)!! / 9 - .9 / .9 = 79
sqrt(9)!! / 9 - 9! / 9! = 79
((9 - sqrt(9))! - 9) / 9 = 79
sqrt(9)!! / 9 - (9 - 9)! = 79

…and 29 more at this tier.

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

Make 78 with four 9s · Make 80 with four 9s

The Number Lab

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

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