Make 70 with four 9s

The classic four nines puzzle: build an expression from exactly four 9s that equals 70. 70 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 70 — the solver checked every possible expression.

Solutions with concatenation and decimals

Concatenation and decimals do not help for 70 either — every combination was checked.

Solutions with square roots, factorials, exponents

sqrt(9)!! / 9 - 9 / .9 = 70
(9 + 9 × sqrt(9)!) / .9 = 70
(sqrt(9)!! - 9) / 9 - 9 = 70
9! × 9 / sqrt(9)! ^ sqrt(9)! = 70
9 × 9! / sqrt(9)! ^ sqrt(9)! = 70

…and 6 more at this tier.

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

Make 69 with four 9s · Make 71 with four 9s

The Number Lab

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

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