# Do you add first or round first?

**first**step in estimating a sum or a difference is

**to round**the numbers, by changing them

**to**the nearest power of ten, hundred, thousand, etc.

**Round**the numbers

**first**, then use mental math

**to**estimate an answer. When rounding, follow these rounding rules: If the number being

**rounded**is less than 5,

**round**down.

Keeping this in view, do you round before or after adding?

As **you can** see, in finding a **round** sum, it is quickest to **round** the numbers **before adding** them. 1. Some statisticians prefer to **round** 5 to the nearest even number. As a result, about half of the time 5 **will** be **rounded** up, and about half of the time it **will** be **rounded** down.

Furthermore, do you round when adding significant figures? When **you add** or subtract, **you** assign **significant figures** in the answer based on the number of decimal places in each original measurement. However, the 35.7 miles measurement extends only to the tenths place. Therefore, **you round** the answer to the tenths place, from 671.05 to 671.1 miles.

Accordingly, what is the Sigfig rule for addition?

Your answer cannot be MORE precise than the least precise measurement. For **addition** and subtraction, look at the decimal portion (i.e., to the right of the decimal point) of the numbers ONLY. 1) Count the number of **significant figures** in the decimal portion of each number in the problem.

How many significant figures does 100 have?

Scientific Notation

(1) | 1000 | 1x10^{3} -- so one sig fig |
---|---|---|

(2) | 0.001 | 1x10^{-}^{3} -- so one sig fig |

(3) | 100. | 1.00x10^{2} -- so three sig figs |

(4) | 0.00100 | 1.00x10^{-}^{3} -- so three sig figs |

(5) | 100 (with two sig figs) | 1.0x10^{2} -- so two sig figs |