Week 8 - Subtraction
Week 8 - Subtraction Sped 482
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SPED 245 - C02
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This 3 page Class Notes was uploaded by Morrissette32 on Sunday March 27, 2016. The Class Notes belongs to Sped 482 at Clarion University of Pennsylvania taught by Mrs. Mohney in Spring 2016. Since its upload, it has received 10 views. For similar materials see Direct instruction in Mathematics in Special Education at Clarion University of Pennsylvania.
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Date Created: 03/27/16
Chapter 8 – Subtraction Vocabulary Subtraction – The removal of a subset from a set. Subtraction is the inverse of addition. Subtrahend- Quantity to be taken away. Minuend – Original quantity from which an amount is subtracted. Difference – The quantity remaining after the subtrahend is taken away from the minuend. Renaming – Rewriting a numeral as a greater unit and a lesser unit. Ex. In 75-19, 75 is renamed as 60+15 Borrowing- a term formerly used to describe subtraction with regrouping or renaming. Regrouping – Rearranging a quantity of objects (not numerals) as a greater and lesser unit. Notes: Two stages of Subtraction: 1. Introducing the concept, the teacher presents strategies for solving simple subtraction problems with a single digit minuend, such as 9-6=. The strategy at this stage involves semi concrete objects that represent each member in the subtraction problem. After subtraction has been taught, problems with a missing subtrahend can be presented. In these problems all numerals should be below 10 to simplify computation. 2. Multi-digit Operations – Usually begins late in the first grade, students compute basic facts mentally (without semi concrete prompts). Basic subtraction facts are the 100 possible combinations in which a one-digit subtrahend is subtracted from a one- or two-digit minuend and the difference is a one-digit number. Three basic types of column subtraction problem: 1. The problem in which the subtrahend is smaller than the minuend in each column, renaming is not required. 2. One or more columns have a subtrahend, which is larger than the minuend; Such problems require renaming or borrowing, 3. Includes more complex column subtraction facts before problems that require renaming. Included are problems with zeros in the minuend. Crossing-Out Strategy The student first draws the number of lines for the minuend, then subtracts by crossing out the number of lines indicated by the subtrahend. Next the student counts the renaming lines on the other side of the equal. Finally the student writes the numeral representing that set of lines. Pre-skill integrated in the format for the crossing out strategy are crossing out lines and counting the remaining lines. Supervised practice is continued until students can work problems with 80- 90% accuracy. Steps in the crossing out strategy for working missing subtrahend subtraction problems: 1. Students read problem 2. Students draw lines under minuend 3. Students determine the number they must end with on both sides. 4. Students circle three of the seven lines, since they must end with three to make sides equal. 5. Students cross out un-circled lines. 6. Students count crossed-out lines and write numeral in the box. Exercises designed to teach a conceptual understanding of renaming are separated from the exercises to teach the mechanics of working problems to simplify the formats for teaching mechanics. Two ways the strategy for subtraction without renaming is the same as the strategy for addition problems that do not require renaming: 1. Students subtract in the ones column and then in the tens column, 2. Students read the number of tens in the tens column rather than the quantity represented by the numerals. Pre-skills taught before subtraction with renaming is introduced: 1. Place value related skills inherent in reading and writing numerals over 10. 2. Knowledge of at least six facts that can be used for borrowing. 3. Conceptual understanding of renaming. Borrowing format that is designed to teach when renaming is necessary: Present rule: when we take away more than we start with we must rename. Lead students in applying the rule. Should be presented over several lessons. Test on 7 problems asking if we rename. (Can only miss one before moving on) Use mix problem types when introducing renaming problems with zero in the tens column in order to prevent students from developing the misrule of always borrowing when they see a zero in the tens column,
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