2) Fractions: Add & Subtract, Problem Solving
5.NF.A.2
5.NF.A.2
I can solve word problems that involve addition and subtraction of fractions.
I can use number sense and fractions that I know to estimate the reasonableness of answers to fraction problems. Video: Real-World Problems - Adding Fractions Video: Real-World Problems - Subtracting Fractions Practice: Real-World Problems (Add & Subtract Fractions) Example: A farmer planted 2/5 of his forty acres in corn and another 3/10 of his land in wheat. Taken together, what fraction of the 40 acres had been planted in corn and wheat? Use visual fraction models or equations to represent the problem. LearnZillion Video: How to add fractions (with unlike denominators) using area models
Use equations to represent the problem. In the real-world problem above, we read the words "taken together." This suggests we'll add the fractions. What do the fractions mean? 2/5 = the amount of land used to plant corn. 3/10 = the amount of land used to plant wheat. x = the fraction of land used to grow corn & wheat An equation can represent the problem: |
Use benchmark fractions and number sense of fractions to estimate mentally and assess the reasonableness of answers.
Ralph got the following addition problem wrong on a math test: 3/5 + 7/9 = 8/14 Write a note to him explaining why the sum doesn’t make sense using your knowledge of benchmark fractions. One possible answer: 3/5 is a little more than ½. 7/9 is almost one whole (9/9 = 1). Therefore, you can estimate that the answer will be close to 1 ½. Ralph’s answer, 8/14, is less than one (in fact, 7/14 = ½, so you can see that 8/14 is a little more than a half). One half is not close to 1 ½, so Ralph’s answer is not reasonable. CA State Standard 5.NF.A.2:
Use equivalent fractions as a strategy to add and subtract fractions. 2. Solve word problems involving addition and subtraction of fractions referring to the same whole, including cases of unlike denominators, e.g., by using visual fraction models or equations to represent the problem. Use benchmark fractions and number sense of fractions to estimate mentally and assess the reasonableness of answers. For example, recognize an incorrect result 2/5 + 1/2 = 3/7, by observing that 3/7 < 1/2. |