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A Symbol Puzzle

Thinking outside the box

There are many math puzzles that give you a set of numbers and ask you to fill in the symbol that solves it. There is a wide variety of symbols you can put in there, like +, -, /, *, and so on. Here’s a simple example of this type of problem.

Put a symbol between 2 and 3 to get a number that is greater than 2 and less than 3.

However, there are problems of this type that are much more complicated, like the following.

Consider the list 1 2 3 4 5 6 7 8 9 = 10. I can put 7 plus and minus signs between them to generate the following equation:

1 + 2 + 3–4 + 5 + 6 + 78 + 9 = 100

This equation works, and notice that the 7 and 8 are combined into 78 since they don’t have a plus or minus sign between them. Can you solve this equation using only 3 plus and minus signs?

The solutions to both problems are below. Take your time to solve this one! If you peek early, you hurt no one but yourself. Once you look, the problem is gone forever.

If you’re stuck, just play around with different solutions! There are not that many possible arrangements with only 3 plus and minus signs.