Primary Standards:
MAFS.2.MD.1.4 Measure to determine how much longer one object is than another, expressing the length difference in terms of a standard length unit.
MAFS.2.MD.2.5 Use addition and subtraction within 100 to solve word problems involving lengths that are given in the same units, e.g. by using drawings (such as drawings or rulers) and equations with a symbol for the unknown number to represent the problem.
MAFS.2.MD.2.6 Represent whole numbers as lengths from 0 on a number line diagram with equally spaced points corresponding to the numbers 0, 1, 2, … and represent whole-number sums and difference within 100 on a number line diagram.
Connecting Standards:
MAFS.2.MD.1.1 Measure the length of an object to the nearest inch, foot, centimeter, or meter by selecting and using appropriate tools such as rulers, yardsticks, meter sticks, and measuring tapes.
MAFS.2.OA.1.1 Use addition and subtraction within 100 to solve one- and two-step word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions, e.g., by using drawings and equations with a symbol for the unknown number to represent the problem.
Content Knowledge:
In 2nd grade, students apply their understanding of addition and subtraction to solve problems related to measurement. They connect subtraction to comparing lengths (finding a difference) and addition to adding to or combining lengths. Exploring addition and subtraction in a measurement context deepens our students’ understanding of operations and provides them with additional experience to refine their problem-solving skills. In addition to comparing measured lengths, students will also solve addition and subtraction problems with given lengths within 100. Their concrete experiences with measuring to compare lengths of objects will help build understanding enabling their ability to model and solve a word problem with manipulatives (e.g. color tiles) or by drawing pictures. Students should also match or write an equation to represent the problem, using a symbol for the unknown.
In this Unit students also represent whole number lengths on a number line. Connections should be made between the concepts of a number line and a ruler (both have equally spaced points, marked with whole number labels.) Students should also have experience drawing and creating their own number lines, choosing appropriate equally spaced labels depending on the length measurements, e.g. skip counting by 5s or 10s. Students should explain how they solved comparison problems using the number line, such as by modeling jumps of 5s instead of counting single jumps to solve greater differences, e.g. 45 – 26.
GCG 1 – Learning Goal: As a mathematician, I can solve measurement problems
- Step 1: Find the difference in length between two objects (using a standard-length unit)
- Step 2: Solve problems about length
- Step 3: Write an equation with a symbol for the unknown to solve a length problem
GCG 2 – Learning Goal: As a mathematician, I can use a number line to solve problems