I stumbled upon this little brain teaser a few months ago. Since then, I've kept a sheet of paper near my computer that I've added to when something strikes me, and I think I've finally completed it. Here's the puzzle:
- Start with four fours: 4 4 4 4
- Add mathematical operators between and around these four fours so that you end up with equations that equal the numbers 1 through 20.
Hint: You'll have to use six different operators, as well as parentheses, to accomplish this.
Here are my answers. Some of these (the first one, is a good example) have more than one possible answer. I went with the one that involves the fewest HTML codes. (And, yes, some of the parentheses are redundant because of the order of operations, but I think they're also easier to read.)
See if you can figure it out, and then click the link below to see my answers.
- (4 + 4) ÷ (4 + 4)
- 4 × (4 ÷ (4 + 4))
- (4 + 4 + 4) ÷ 4
- (√4 + √4) × (4 ÷ 4)
- ((4 × 4) + 4) ÷ 4
- √4 + 4 × (4 ÷ 4)
- (4 + 4) – (4 ÷ 4)
- 4 + 4 + 4 – 4
- 4 + 4 + (4 ÷ 4)
- 4 + 4 + 4 – √4
- (4! ÷ √4) – (4 ÷ 4)
- (√4 + √4 + √4) × √4
- (4! ÷ √4) + (4 ÷ 4)
- 4 + 4 + 4 + √4
- (4 × 4) – (4 ÷ 4)
- 4 + 4 + 4 + 4
- (4 × 4) + (4 ÷ 4)
- 4! – (√4 + √4 + √4)
- 4! – 4 – (4 ÷ 4)
- (4 × 4) + (√4 × √4)