Download 5.3: Using Combined Difference to Subtract Larger Numbers Across

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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],
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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],
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