CCSS.Math.Content.4.NF.C.5
The standard
Express a fraction with denominator 10 as an equivalent fraction with denominator 100, and use this technique to add two fractions with respective denominators 10 and 100.
Common Core State Standards for Mathematics · Number and Operations—Fractions
What this standard means
Students need to rename tenths as hundredths, then use that common denominator to add fractions. They should see that one tenth is the same amount as ten hundredths, not just add a zero as a trick. Area models, hundred grids, money, and place value language all help connect the symbols to size.
Mastery looks like writing equivalent fractions correctly, adding tenths and hundredths accurately, and explaining why the answer makes sense. Common stuck points are adding denominators, treating 3/10 as 3/100, or following a procedure without seeing the value stay the same.
Ways to teach it
- Have students shade 3 tenths on a hundred grid, relabel it as 30 hundredths, then add 4 more hundredths in another color.
- Ask students to explain in writing why 6/10 and 60/100 cover the same amount of a hundred grid.
- Give four problems like 2/10 + 7/100 and ask students to solve one with a model and one with numbers.
- Use dimes and pennies to show how 4 dimes plus 8 pennies matches 40/100 plus 8/100 of a dollar.
Plan a lesson for CCSS.Math.Content.4.NF.C.5
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Related standards
- CCSS.Math.Content.3.NF.A.3c
Express whole numbers as fractions, and recognize fractions that are equivalent to whole numbers.
- CCSS.Math.Content.5.NF.A
Use equivalent fractions as a strategy to add and subtract fractions.
- CCSS.Math.Content.4.NF.C.6
Use decimal notation for fractions with denominators 10 or 100.
- CCSS.Math.Content.4.NF.A.2
Compare two fractions with different numerators and different denominators, e.g., by creating common denominators or numerators, or by comparing to a benchmark ...