The Four Fours
Here is an interesting math puzzle that you can play just about anywhere. All you really need is paper and a writing instrument. A calculator is not needed, but it is highly recommended! The rules of this puzzle are simple enough, although there are some variants. The rules given here are the ones I was given when I first learned of this math puzzle.
Using four fours, you are to find a mathematical expression for every whole number you can starting with zero. You can use addition, subtraction, multiplication, division, factorials, decimal points, exponents, 0.4bar (i.e., the recurring decimal 0.44444. . .), and square roots. Use of parentheses to emphasize the order of operations is not only allowed, but encouraged!
Some examples are:
0 = (4 + 4) – (4 + 4)
17 = (4 x 4) + (4 ÷ 4)
The Four Fours puzzle (a.k.a., The Four Fours Problem) has been known for years, and was described by Walter William Rouse Ball in his publication “Mathematical Recreations and Essays”:
Often times, there are multiple possible solutions. How many can you find?