1. Rounding And Estimating

2. Rounding Decimals You can round decimal numbers when you don’t need exact values. Review: 38.41 0.7772 7,098.56 274.9434 5.025 9.851 Tenth, 38.4 Ones, 1 Tenths, 7,098.6 Thousandths, 274.943 Tenths, 5.0 Hundredths, 9.85

3. Estimating Sums and Differences You can estimate an answer before you calculate, to make sure your answer is reasonable. The symbol  means “is approximately equal to.” One way to estimate is to round all of the numbers to the same place value.

4. Front-End Estimating 1) Gets you closer to the exact sum than estimating by rounding. 2) Add the front-end digits. (to the left of the decimal) 3) Round to estimate the sum of the remaining digits (to the right of the decimal) 4) Combine the two estimates. (add)

5. Front-End Estimating Use Front-End Estimating: $1.10 $1.73 $2.71 $4..10.73.71. ? Estimate by Rounding..10.70 1.50 Now add, $4 + $1.50 = $5.50 The total cost is about $5.50.

6. Try This: Estimating using Front-End Estimation. 6.75 + 2.2 + 9.58 = about… $1.04 + $2.49 + $7.40 = about…

7. Clustering Use clustering to estimate the sum of several numbers that are close to one value. Example: Phone Bills for 4 Months May: $15.35 June: $16.05 July: $14.90 August: $15.05 What dollar amount do the 4 bills cluster around? $15.00 is our cluster value. 4 bills at,  $15 means 4 $15 = $60 is  the total cost.

8. Try This: Using Cluster Estimating $4.50 + $5.20 + $5.55 = 26.7 + 26.2 + 24.52 + 25.25 + 23.9 = About $15 About 125

9. Estimating Quotients: Things to Remember Dividend Divisor Quotient Compatible Numbers: numbers that are easy to divide mentally. 24  8 = 3

10. Estimating Quotients 1)Round the divisor. 2)Round the dividend to a compatible number. 39.9  1.79  11.95  2.1  1.79  2, 39.9  40, so 40  2 20 2.1  2, 11.95  12, so 12  2 6