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RAMP 5.3 Place Value/Base Ten: Grades 1– 2 Objective: Students will use the subtraction strategy Combined Notes Difference to subtract larger numbers across 10 Using Combined Difference to Subtract Larger Numbers Across 10 In 5.3, students will employ Distance From Ten strategies and Combined Difference strategies to solve subtraction problems for larger numbers. In 5.2, they established a procedure (combine the difference above and below 10 to get the answer). They then practiced this procedure with smaller numbers they know. In 5.3 they begin to solve subtraction problems for larger numbers they don’t know as well, using the same procedure, applying a more complex version of the strategy distance from 10. START By reviewing strategies for solving subtraction problems near 10, and fact families for larger numbers. ASK Students to solve 16-8. ASK What is the tens fact for 16? 16 is 6 away from 10, because the 10s fact is 6+4. ASK What is the tens fact for 8? 8 is 2 less than 10, because the 10s fact is 8+2. Last revised 01/09/2010 2009University Place School District. All rights reserved. The Math: Getting It Project is a Mathematics and Science (MSP) Partnership funded by the Department of Education. Partners: University Place School District (lead partner), Peninsula School District, and Fife School District; the University of Washington/Tacoma; and the Pierce County Staff Development Consortium, Pierce County, Washington. For more information, contact the Math:Getting Project Co-Directors, Jeff Loupas [email protected] or Annette Holmstrom [email protected], 1 RAMP Place Value/Base Ten: Grades 1– 2 DO have students graph each number using a floating number line, indicating the distance from 10: ASK So when you combine the differences, what do you have? Combine the Differences: 16 - 8 = 6 + 2 DO Write the answer: 8 SHOW the illustration for another subtraction math problem using larger numbers on the floating number line graph: 13 – 7, for example. DO Have students solve this subtraction problem following these steps: Step 1: Use knowledge of 10s facts to figure out how far the first number is from 10. (In the subtraction problem 13 – 7, the number 13 is 3 more than 10.) Step 2: Use knowledge of 10s facts to figure out how far the second number is from 10. (In the subtraction problem 13 -7, the number 7 is 3 less than 10). Step 3: Combine the difference from 10. (The difference from 10 of the number 13 (3) is combined with the difference from 10 of the number (3) to find the answer: 3 + 3 = 6 So 13 – 7 = 6). DO model this strategy multiple times until students are comfortable solving subtraction problems in which larger numbers cross the 10 (refer to list of problems at the start of this lesson). DO model and have students write subtraction number sentences to match graphs they’ve made for combined difference problems. (13-9). DO Practice and reinforce with 5.3 worksheets. Last revised 01/09/2010 2009University Place School District. All rights reserved. The Math: Getting It Project is a Mathematics and Science (MSP) Partnership funded by the Department of Education. Partners: University Place School District (lead partner), Peninsula School District, and Fife School District; the University of Washington/Tacoma; and the Pierce County Staff Development Consortium, Pierce County, Washington. For more information, contact the Math:Getting Project Co-Directors, Jeff Loupas [email protected] or Annette Holmstrom [email protected], 2