Significant Figures in Derived Results:  Addition & Subtraction

1. Find the last significant digit in each number to be added or subtracted (the colored numbers below).
2. Determine which number has the greatest uncertainty.  It will be the one with the last significant digit farthest to the left in the column of numbers.
3. In the number with the greatest uncertainty, the place of the last significant digit represents the place of the last significant digit in the final answer. 

The answer must be rounded so that it contains the same number of digits to the right of the decimal point as there are in the measurement with the smallest number of digits to the right of the decimal point.

In the examples below, the significant figures are colored blue and the uncertain digits are bold.

              7003                                                             347.2

              21.2                                                            -    140

        +  130.00                                                               207.2     =  210

  7154.20     =  7154                                         The tens place. 1, is the last place a digit it kept in                                                                                          the final answer.  The zero is a place holder.

The ones place, 4, is the last place a digit is kept in the final answer.