Rounding Numbers - review

Post date: Mar 22, 2010 8:26:2 PM

When rounding whole numbers there are 2 rules to remember:

I will use the term rounding digit - which means: When asked to round to the closest tens - your rounding digit is the second number to the left (ten's place) when working with whole numbers. When asked to round to the nearest hundred - the third place from the left is the rounding digit (hundreds place).

Rule 1. Determine what your rounding digit is and look to the right side of it. If the digit is 0,1,2,3 or 4 do not change the rounding digit. All digits that are on the right hand side of the requested rounding digit will become 0

Rule 2. Determine what your rounding digit is and look to the right of it. If the digit is 5,6,7, 8 or 9, your rounding digit rounds up by one number. All digits that are on the right hand side of the requested rounding digit will become 0

Rounding with decimals: When rounding numbers involving decimals, there are 2 rules to remember:

· Rule 1. Determine what your rounding digit is and look to the right side of it. If that digit is 4,3, 2 or 1, simply drop all digits to the right of it.

· Rule 2. Determine what your rounding digit is and look to the right side of it. If that digit is 5, 6, 7, 8 or 9 add one to the rounding digit and drop all digits to the right of it.

· Rule 3: Some teachers prefer this method:

This rule provides more accuracy and is sometimes referred to as the 'Banker's Rule'. When the first digit dropped is 5 and there are no digits following or the digits following are zeros, make the preceding digit even (i.e. round off to the nearest even digit). E.g., 2.315 and 2.325 are both 2.32 when rounded off to the nearest hundredth. Note: The rationale for the third rule is that approximately half of the time the number will be rounded up and the other half of the time it will be rounded down.

Examples:

765.3682 becomes:

1000 when asked to round to the nearest thousand (1000)

800 when asked to round to the nearest hundred (100)

770 when asked to round to the nearest ten (10)

765 when asked to round to the nearest one (1)

765.4 when asked to round to the nearest tenth (10th)

765.37 when asked to round to the nearest hundredth (100th.)

765.368 when asked to round to the nearest thousandth (1000th)

View these Rounding Numbers worksheets for more information

When finished, compare your answers with these! How did you do?