Concepts

Rounding is approximating a number to a given place value.

Rules

Consider the place value you are rounding the number to.
If the number to the right of the digit being rounded is 5,6,7,8, or 9, round the number up. If the number to the right of the digit being rounded is 0,1,2,3, or 4, round the number down.

Example

Estimate 11 + 28

Solution

Round 11 to the nearest ten.
If the digit in the ones place is less than 5, round the number down to 10. Otherwise, round the number up to 20. 
The answer is 10

Round 28 to the nearest ten.
If the digit in the ones place is less than 5, round the number down to 20. Otherwise, round the number up to 30. 
The answer is 30.

Add 10 and 30 to find the estimated sum.

The answer is 40.

Prerequisite Skills

Compare Whole Numbers (4.1.9)

Points on a Number Line (4.12.4)