Addition and Subtraction
In this chapter you will learn to:
- Use addition properties and subtractions rules.
- Estimate sums and differences.
- Determine when to estimate or find an exact answer.
- Add and subtract whole numbers, including multi-digit numbers.
Properties of Addition
- The Commutative Property of Addition: The order in which numbers are added does not change the sum. For example: 4 + 1 = 5 and 1 + 4 = 5.
- The Associative Property of Addition: The way in which numbers are grouped when added does not change the sum. For example: (5 + 2 ) + 3 = 5 + (2 + 3).
- The Identity Property of Addtition: The sum of any number and 0 is the number. For example: 8 + 0 = 8 or 0 + 8 = 8.
Subtraction Rules
- When you subtract 0 from any number, the result is the number. For example: 6 - 0 = 6 or 4 - 0 = 4.
- When you subtract any number from itself, the result is 0. For example: 6 - 6 = 0 or 5 - 5 = 0.
Estimation
- Sometimes you do not need an exact answer. When the word about is used in a problem, you can find an estimate. An estimate is an answer close to the exact answer.
- You can round to estimate by following these rules. To round a number, underline the place you want to round to. Look at the place to the right. If the digit is 5 or more, round up to the next number. If it is less than 5, the number stays the same. Put zeroes in the places to the right of the underlined number. For example: 37 is rounded to 40 because the 7 to the right of the 3 is more than five. 21 is rounded to 20 because the 1 to the right of the 2 is less than 5.
- When adding or subtracting you may need to regroup.
No comments:
Post a Comment