Rounding whole numbers and Decimals

1. Rounding whole numbers and Decimals

2. The purpose of rounding… • Why do we use rounding? • We round numbers to make them shorter or simpler. • Can you think of a scenario when we would need to make a number shorter? • Anytime we need to estimate or get an approximate number, rounding should be used. • For example: You are at the mall and only have $30. Your lunch is $5.95, you buy a game for $19.99, and you want to see a movie that costs $8.50…do you have enough money?

3. Rules for rounding whole numbers… • Determine which digit (the place value) is your rounding number and underline it. • Look to the right of the underlined number: *if the number to the right is 0,1 , 2, 3,or 4, then you do not change the rounding digit and all other digits to the right become zeros. *if the number to the right is 5, 6, 7, 8, or 9, then you add 1 to the rounding digit and all other digits to the right become zeros. Examples: 6, 5 3 2 this now becomes 6, 5 3 0 1 0, 7 9 4 this now becomes 11, 000

4. Rules for rounding decimals… • Underline the rounding digit and look to the number on the right. • If the number is 0, 1, 2, 3, or 4, then you do not change the underlined number and delete all of the other numbers to the right. • If the number is 5, 6, 7, 8, or 9, then you add 1 and drop all of the other numbers to the right. *the numbers in front of the underline number always stay the same, unless you add 1 to the number 9. Example: 53.864 becomes 53.86 603.5678 becomes 603.6 45.698 becomes 45.7

5. Ready, set, go… • Now let’s practice a few problems together