4.2

1. Adding and Subtracting Decimals 4.2

2. Adding and Subtracting Decimals Adding or Subtracting Decimals Step 1: Write the decimals so that the decimal points line up vertically. Step 2: Add or subtract as with whole numbers. Step 3: Place the decimal point in the sum or difference so that it lines up vertically with the decimal points in the problem.

3. 85.00- 13.26 Helpful Hint Recall that 0s may be inserted to the right of the decimal point after the last digit without changing the value of the decimal. This may be used to help line up place values when adding or subtracting decimals. 85 - 13.26 becomes two 0s inserted 71.74

4. Adding Decimals

5. Example Add: 756.23 + 26.504 + 1.087 Insert one zero 783.821

6. Example Subtract: 56.21 – 5.9 Insert decimal point and one zero

7. Example Subtract: 28 – 3.3 Insert decimal point and one zero Line up decimal points 24.7 Subtract.

8. Estimating when Adding or Subtracting Decimals To help avoid errors, we can estimate to see if our answer is reasonable by rounding the given numbers and adding or subtracting. Example: 7.6 – 2.1 Exact rounds to rounds to Since the exact answer is close, it is reasonable.

9. Estimating When Adding Decimals Add 23.8 + 32.1. Exact Estimate rounds to rounds to This is a reasonable answer.

10. Example A pair of eyeglasses costs a total of $347.89. The frames of the glasses are $97.23. How much do the lenses of the eyeglasses cost? The lenses of the eyeglasses cost $250.66.

11. Helpful Hint When rounding to check a calculation, you may want to round the numbers to a place value of your choosing so that your estimates are easy to compute mentally.

12. Evaluating with Decimals Evaluate x + y for x = 5.5 and y = 2.8. Replace xwith 5.5 and y with 2.8 in x + y. 2.8 x + y= ( ) + ( ) 5.5 = 8.3