Slide 1Slide 2AnnoundaPictorial ModelsPictorial ModelsNumber Line ModelFour related factsSubtraction & Addition do we NEED both?Mental SubtractionMental SubtractionExploration 3.1 (p. 50)Week 4In your head, compute:65 - 2871 - 3980 - 36Explain what you did so that a second grader will understand.Announda• Don’t forget to initial attendance sheet!•Exam 1 is one week from today!•Some practice questions will be posted online.•Monday Office Hour: Rescheduled to 12:00-1:00pm in MATHE LOBBY•Subtraction ContinuedPictorial Models•Take away•Judy has 7 crosses and gives 2 to Jake. How many does Judy have left?Pictorial Models•Comparison•Amy has 7 crosses and Andy has 2. How many more crosses than Andy does Amy have?Number Line Model•7 - 9 = -2•Why is it important to start at 0?-2 -1 0 1 2 3 4 5 6 7 8 9 10Four related facts•If 9 - 4 = 5, then9 - 5 = 4, 4 + 5 = 9, and 5 + 4 = 9•You try: If 74 - 61 = 13, then …Subtraction & Addition do we NEED both?Mental Subtraction•65 – 28Mental Subtraction•Not as obvious as mental addition•65 - 28Break apart the second number (65 - 20) - 8•Adding up 28 + 30 = 58, 58 + 7 = 65, 30 + 7•Compensation (65 + 2) - (28 + 2)•Compatible Numbers (65 - 25, add back 3)Exploration 3.1 (p.
View Full Document
Unlocking...