Activity You can use base-ten pieces to model decimal addition and subtraction. 1Model the sum of 0.76 and 0.58 using base-ten pieces. 2 Combine and group the pieces. 3Trade 10 tenths for 1 one and 10 hundredths for 1 tenth = 1.34 Adding and Subtracting Decimals 2.

EXAMPLE 1 Adding and Subtracting Decimals SOLUTION ––––––– + 0 Adding and Subtracting Decimals 2. Use a vertical format to add or subtract decimals. Begin by lining up the decimal points. Then add or subtract as you would with whole numbers. Be sure to write the decimal point in the answer. Write zero as a placeholder.

– EXAMPLE 1 Adding and Subtracting Decimals SOLUTION ––––––– + –––––– –.00 0 Adding and Subtracting Decimals 2. Use a vertical format to add or subtract decimals. Begin by lining up the decimal points. Then add or subtract as you would with whole numbers. Be sure to write the decimal point in the answer. SOLUTION Write zeros as placeholders. Write zero as a placeholder.

Evaluate r – t when r = 2.14 and t = r – t Substitute 2.14 for r and 5.2 for t. Add. = – 5.2 = 3.64 Subtract. EXAMPLE 2 Evaluating a Variable Expression SOLUTION Adding and Subtracting Decimals 2. = r – t

Estimation When you do not need to find an exact sum, you can estimate. One type of estimation is front-end estimation. To use front-end estimation to estimate a sum, add the front-end digits, estimate the sum of the remaining digits, and then add the results. Adding and Subtracting Decimals 2.

Video Games For your birthday you receive a $ 25 gift certificate. You want to buy 3 used video games whose prices are shown. Can you buy all 3 games using the gift certificate? 123 Add the front-end digits: the dollars. $8.79 $7.29 $7.89 $22 $8.79 $7.29 $7.89 Estimate the sum of the remaining digits: the cents. $1$1 $1$1 __ Add the results. $22 $2$2 $2$2 $24 EXAMPLE 3 Estimating a Sum ––––––– + + –––– + Adding and Subtracting Decimals 2. ANSWER The estimated sum is less than $25, so you can buy all three games using the gift certificate. SOLUTION