burger fun / Four Fours / Solver

Make 15 with four 4s

The classic four fours puzzle: build an expression from exactly four 4s that equals 15. 15 can be made with nothing but four 4s, + - × ÷, and parentheses.

Solutions using only + - × ÷

• 4 × 4 - 4 / 4 = 15

Solutions with concatenation and decimals

• 4 + 44 / 4 = 15
• 4 + 4.4 / .4 = 15
• 4 × 4 - .4 / .4 = 15
• (.4 + 4) / .4 + 4 = 15
• (4 / .4 - 4) / .4 = 15

Solutions with square roots, factorials, exponents

• 4 × 4 - 4! / 4! = 15
• 4 × 4 - (4 - 4)! = 15
• (4 - 4 / 4)! / .4 = 15
• (.4 - 4) / .4 + 4! = 15
• 4! - (4 - .4) / .4 = 15

…and 216 more at this tier.

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

Make 14 with four 4s · Make 16 with four 4s

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

Read up on the 1881 original, pick another number in the solver, or find more free math games.