burger fun / Four Nines / Solver

Make 80 with four 9s

The classic four nines puzzle: build an expression from exactly four 9s that equals 80. 80 can be made with nothing but four 9s, + - × ÷, and parentheses.

Solutions using only + - × ÷

• 9 × 9 - 9 / 9 = 80

Solutions with concatenation and decimals

• 9 × 9 - .9 / .9 = 80
• (9 × 9 - 9) / .9 = 80

Solutions with square roots, factorials, exponents

• 9 × 9 - 9! / 9! = 80
• 9 × 9 - (9 - 9)! = 80
• 9 × 9 - (.9 - .9)! = 80
• 9 × 9 - (9! - 9!)! = 80
• (9 ^ sqrt(9) - 9) / 9 = 80

…and 703 more at this tier.

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

Make 79 with four 9s · Make 81 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
• Four Fours — the 1881 original
• Four Fours solver — including the impossible five
• Make 24 solver — any four digits
• 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.