Sum of 18.0 and 12.60 is correctly reported as

$18.0+12.60 =30.60 ;$ It is reported as $30.\underset{-}{6}$. The result cannot have more digits to the right of the decimal point than either of the two original numbers. In this case the result must have only one digit after decimal point as the least number of digits after decimal point in the original numbers is one. (present in the original number $18.\underset{-}{0}$)