Number System

  
Fill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!
1. (-30) + = 60.

2. (-5) + () = -100.

3. + (-22) = 0.

4. + (-70) = 70.

5. 20 + 80 + () = 0.

6. 75 + (-25) = .

7. 171 + () = 0.

8. [(-3) + (-12)] +(-77) = () + [(-12) + (-77)]

9. (-42) + [ + (-23)] = [() + 15] + ().

10. (-52) + (-52) = .