The operation with decimals that requires you to count place value to place the decimal in the answer is multiplication. When multiplying decimal numbers, you multiply as if they are whole numbers and then count the total number of decimal places in both of the original numbers. This total indicates where to place the decimal point in the final answer.
For example, if you multiply 3.4 (which has one decimal place) by 0.2 (which also has one decimal place), you treat it as 34 x 2 = 68. Then, since there are a total of 2 decimal places in the factors, you place the decimal point two places from the right in the result: 68 becomes 0.68.