The third grade mathematics volume: the average score of five numbers is 60. If one of the numbers is changed to 80, the average value becomes 70. What was the original number?
The average of five numbers is 60. If one of the numbers is changed to 80, the average value becomes 70. What was the original number?
A: 70-60 =105x10 = 50 80-50 = 30, so this number was originally 30.