The average of 10 items was found to be 80 but while calculating, one of the items was counted as 60 instead of 50. Then the correct average would have been :

Answer: Option C

Accounting to the question,
Incorrect number = 60
Correct number = 50
Difference = 60 - 50 = 10 (more)
Difference '10' effects all the 10 items
= $$\frac{10}{10}$$
= 1
Old average = 80
New average = 80 - 1 = 79