Five pages on adding and subtracting mixed numbers whose fractions have different denominators, with denominators up to 12. Page 1 adds by parts: add the wholes, rewrite the fractions with a common denominator and add them, so 1 1/4 + 2 1/3 = 3 + 3/12 + 4/12 = 3 7/12. When the fractions make more than 1, rename: 2 3/4 + 1 1/3 = 3 + 13/12 = 4 1/12, shown on fraction strips cut into twelfths. Page 2 adds in columns, then simplifies and renames the sum. Page 3 subtracts by parts with no trading, then gives problems with room to work. Page 4 trades 1 whole when the top fraction is too small: 6 1/5 − 3 1/2 is shown counting back on a number line and in columns (6 2/10 = 5 12/10), and whole numbers are traded too (6 = 5 12/12). Page 5 estimates with whole numbers before solving, has students find the mistake in another student's work, and ends with two story problems. Every page starts with a worked example.
Before page 1, ask what 1 1/4 + 2 1/3 is about: a little more than 3. Then ask why the 1/4 and the 1/3 cannot simply be added, and cut both into twelfths. Before page 4, show 6 1/5 with six whole strips and a fifth, then trade one whole for ten tenths so there are enough tenths to take away 1/2. On page 5, have students say the estimate out loud before they work anything out.
Recipes and measuring are full of mixed numbers: 2 1/2 cups of flour and 1 2/3 cups of sugar, or a board 6 1/4 feet long with 2 1/3 feet cut off. Ask your child for a quick estimate first, then work out the exact amount together.
This pack supports the following Common Core State Standards for Mathematics:
© Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
Adding and subtracting mixed numbers whose fractions have different denominators. Students rewrite the fractions with a common denominator, add and subtract by parts and in columns, rename and trade 1 whole, and check their answers with estimates.
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