Sally made a 50 average for the first nine weeks. She currently has a 70 average for the second nine weeks. Sally knows that she needs a bo to pass the fall semester. So she takes her calculator and enters 50 + 70 : 2. She tells Mr. Waddle that she has an 85 average. Mr. Waddle tells her, "Sally, you will pass the semester but your actual average is much'less than the 85 you got on your calculator." What did Sally do wrong?