Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.

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Ages: 7 - 10
Addition 2 - Khan Academy
From YouTube, produced by Sal Khan
In this video, the instructor uses software to review how to add numbers. He starts with single-digit numbers, then moves into two-digit numbers, and reviews how to use a number line. (12:26)
January 27, 2010 at 02:36 AM
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Not Right For WatchKnowLearn
Ages: 7 - 10
Basic Addition on a Black Board
From gamequarium.org
This video introduces the basic concept of addition. One digit addition is demonstrated using two methods. Adding is first demonstrated by combining objects to get a total. Addition is also demonstrated using a number line and moving forward on that ... [more]
Found by begamatt in 1.NBT.C.5
August 1, 2010 at 10:52 PM
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