[ Mathematics ] Open Question : how do you solve this math problem?

So, I am practicing integers and i came across this question: (+12) - (-12) I think the answer is 0 because when you have 2 integers that have the opposite signs you subtract the larger number from smaller but everytime i punch it in the calculator i get 24. Can someone explain to me why this is? thankyou and answer asap

Source: http://answers.yahoo.com/question/index?qid=20110825105931AAPaMJY

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