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Expectations from the Number and Operations Standard Principles and Standards for School Mathematics National Council of Teachers of Mathematics 2000
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Understand numbers, ways of representing numbers, relationships among numbers, and number systems. Grades 6-8 Develop meaning for percents greater than 100 and less than 1. Understand and use ratios and proportions to represent relationships
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Compute fluently and make reasonable estimates. Develop, analyze, and explain methods for solving problems involving proportions, such as scaling and finding equivalent ratios. 4’ 12’
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Ratio-relationship between 2 quantities. 3 games for 50 cents 3/50 3 to 503:50
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Proportion-equal ratios Joe will often tape 6 minutes of audio tape to obtain enough footage for a 30-second music clip. At that rate, how many minutes of tape will it take to shoot a 45-second music clip? 6 tape =N tape 30min = 45min cross multiply: 30 x N = 6 x 45 30 x N = 270 N=9
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Percent-per 100 a special ratio N/100 25/100=.25=25% Prerequisite skills Decimals fractions multiplication equations/variables-find missing numbers
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Percent Shortcuts A% of B = B% of A Ex: 28% of 50 = 50% of 28 (KA)% of B = K(A% of B) Ex: 20% of 35 is twice 10% of 35 (2x10)% of 35 = 2(10% of 35) Source: Glatzer, Arithmetic Teacher, Feb. 1994
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Percent Shortcuts (A+C)% of B = (A% of B) + (C% of B) Ex: 15% of 60 = (10% of 60) + (5% of 60) Source: Glatzer, Arithmetic Teacher, Feb. 1994
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Tangrams and Percent Find the area of each of the seven tangram pieces using a ruler or grid paper. Record your results. What is the total area of all seven tangram pieces? Find what percent of the whole area each piece is. Record your results.
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Jacob: Fourth Month of Seventh Grade
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Jacob: Fourth Month of Seventh Grade (con’t)
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Bradley: Fourth Month of Seventh Grade
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Allan: Fourth Month of Seventh Grade
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Jessica: Fourth Month of Seventh Grade
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