alberto: what -31+15=16
right
Think of it like this
The temperature is -31 degrees, it gets warmer by 15 degree, has it reached 0 yet or is it just closer to 0 (that is, less negative)?
It would have to warm up by 31 degrees before it got to 0 so it must just be 'less negative'.
So the answer is negative but closer to zero than -31.
31-15=16
so
-31+15 must be -16
+118653 
