# Representing & Solving Problems with Addition and Subtraction

Learning how to solve one- and two-step word problems using addition and subtraction is a second grade, Common Core math skill: 2.OA.1. Below we show two videos that demonstrate each of these standards. Then, we provide a breakdown of the specific steps in the videos to help you teach your class.

Prior Learnings

Your students should be experienced in solving all types of addition and subtraction problems. Before, “addition” was separate from subtraction and the problems were limited to one-step problems and numbers within 20 (1.OA.1).

Future Learnings

After learning these math skills, your students will be able to apply strategies to both one and two-step problems that involve the “four operations (addition, subtraction, multiplication, division).” Additionally, your students will learn how to represent an unknown using a letter (3.OA.8).

Common Core Standard: 2.OA.1 - Use addition and subtraction within 100 to solve one- and two-step word problems

Students who understand this principle can:

1. Identify the unknown number in an addition or subtraction word problem.
2. Determine the correct operation to solve addition and subtraction problems in various situations (e.g. add to, take from, put together, take apart, and compare).
3. Use drawings/equations to represent and solve one- and two-step word problems.
4. Add and subtract within 100 to solve one-step word problems with unknowns in all positions.
5. Write an addition and subtraction equation with a symbol representing the unknown factor.

Video 1: One- and Two-Step Word Problems

This video is aimed at teachers (not students) and breaks down the components of the standard 2.OA.1, offering examples of 1 and 2 step problems.

First, the video introduces the standard and lists the parts related to the standard.

1. Word problems
2. Add and subtract numbers under 100
3. Can have 1 or 2 steps to the problem
4. Answer may not be the sum or difference but in the problem itself (i.e. 3 + ? = 5)
5. Can be solved with both standard math equations and with drawings

Next, the video gives an example of a 1-step word problem: “James’ class has an ice cream party. He watches his teacher serve 11 ice cream cones. There are 19 students in James’ class. How many more ice cream cones does his teacher need to serve?

1. 11 + ? = 19
2. Using related equations (fact families) students should be able to rewrite the problem.
3. 19 - 11 = ?
4. Pictures are used to demonstrate the problem

In either the standard equation method or the drawing method, students should get the answer 8, whether through drawing pictures or using mental subtraction skills.

Next, the video shares an example of a 2-step word problem, similar to the first problem: “James’ class has an ice cream party. There are 19 students in James’ class. He watches his teacher make 11 ice cream cones. 3 ice cream cones melt. How many more ice cream cones does his teacher need to make for each student to get an ice cream?

1. 11 - 3 + ? = 19
2. First, we complete the subtraction problem.
a. 11 - 3 = 8
3. 8 + ? = 19
4. One can solve this using related equations.
a. 8 + ? = 19
b. ? + 8 = 19
c. 19 - ? = 8
d. 19 - 8 = ?

The video ends by advising teachers to give their students additional word problems to solve. Once students understand how to solve these word problems successfully, you can have them create word problems for their classmates to solve.

Video 2: Adding with Paul and Subtracting Ribbon Lengths

Boddle introduces the mathematical topic before heading into a classroom where we meet a student named Paul.

Some of Paul’s classmates notice his backpack is really heavy, and he shows them what’s inside:

• 6 notebooks
• 3 textbooks
• 5 pencils
• 8 crayons

Boddle then asks how many items are in Paul’s backpack. To solve the problem, one must use addition.

1. First, write an equation to represent the problem.
2. 6 + 3 + 5 + 8 = ?
3. To simplify, add 2 numbers at a time.
4. 6 + 3 = 9
5. 5 + 8 = 13
6. Then add those 2 new numbers to find the total number of items.
7. 9 + 13 = 22

Paul has 22 items in his bag. No wonder it’s so heavy!

After, Boddle uses subtraction to solve a math problem involving two rolls of ribbon.

1. The first roll is 85 cm long when it is unrolled.
2. The second roll is 63 cm long when it is unrolled.
3. What is the difference? (Boddle reminds students what difference means in math.)
4. 85 cm - 63 cm = the difference

Boddle shows students that the easiest way to solve this problem is by moving the numbers so their place values are lined up in columns.

After the numbers are aligned correctly, Boddle starts by subtracting the numbers in the ones place.

1. 5 - 3 = 2
a. Make sure the answer goes under the ones column.
b. Then move on to the tens place.
2. 8 - 6 = 2
3. The difference between the lengths of the two rolls of ribbon is 22 cm.

Boddle says goodbye, congratulating the students on a job well done!

Want more practice?