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Rounding Objective: •Round two-digit numbers to the nearest ten. •Round three-digit numbers to the nearest hundred. •Estimate sums and differences. Rounding two-digit numbers Two-digit number will be rounded to the nearest ten. 26 So we can say that the number 26 is closer to 30 than to 20. 30 RULES FOR ROUNDING 1. Underline the number in the place value you will round. 2. Look at the number to the right of the underlined number. 3. If the number to the right is 0, 1, 2, 3, or 4, then the underlined number stays the same. 4. If the number to the right is 5, 6, 7, 8, or 9, then the underlined number needs to go up one more number. 5. Every number to the right of the underlined number becomes a zero. Rounding three-digit numbers Three-digit number will be rounded to the nearest hundred. 520 500 So we can say that the number 520 is closer to 500 than to 600. RULES FOR ROUNDING 1. Underline the number in the place value you will round. 2. Look at the number to the right of the underlined number. 3. If the number to the right is 0, 1, 2, 3, or 4, then the underlined number stays the same. 4. If the number to the right is 5, 6, 7, 8, or 9, then the underlined number needs to go up one more number. 5. Every number to the right of the underlined number becomes a zero. 26 is closer to 30 than to 20. 20 26 30 520 is closer to 500 than to 600. 500 520 600 Estimating sums First, round all the numbers using the RULES FOR ROUNDING Then, perform the operations. 12 + 8 ------- 10 + 10 ------20 Estimating differences First, round all the numbers using the RULES FOR ROUNDING Then, perform the operations. 25 - 11 ------- 30 - 10 ------20 RULES FOR ROUNDING 1. Underline the number in the place value you will round. 2. Look at the number to the right of the underlined number. 3. If the number to the right is 0, 1, 2, 3, or 4, then the underlined number stays the same. 4. If the number to the right is 5, 6, 7, 8, or 9, then the underlined number needs to go up one more number. 5. Every number to the right of the underlined number becomes a zero. Now you practice. Round these numbers. 25 78 36 158 689 324 30 80 40 200 700 300 Practice rounding sums and differences 25 30 - 15 - 20 ------------12 + 36 ------- 10 + 40 ------- 128 + 42 ------- 100 + 40 ------- MCT2 Preparation Sample Question The cafeteria is selling ice cream cones for 23¢ and ice cream sandwiches for 48¢. If Ms. Rodriguez buys an ice cream cone and an ice cream sandwich, about how much money will she spend? $1.00 70 ¢ 50 ¢ 25 ¢