A problem which crops up quite often in puzzles is that of inserting mathematical signs wherever one cares to between the digits 1,2,3,4,5,6,7,8, and 9 to make the resulting expression equal in value to 100. The digits must remain in the same sequence. One of the numerous solutions to this problem is: 1+2+3+4+5+6+7+(8x9)=100

The problem becomes slightly more difficult if only plus and minus signs are allowed. A typical solution to the problem now is this: 12+3-4+5+67+8+9=100 In this solution, six plus and minus signs were used.

Can you find a solution to this plus-and-minus-only problem using three signs?

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