Lesson 3: Addition and Subtraction Word Problems

New Concept

Mathematics uses predictable patterns, or "plots," to solve real-world problems. By identifying the plot, we can select the correct formula to find the solution.

What’s next

To begin, we will apply this method to addition and subtraction problems. You'll work through examples involving combining, separating, and comparing quantities.

Property

some + more = total ($s + m = t$)

Examples

• $12 \text{ points} + m = 27 \text{ total points} \rightarrow 27 - 12 = 15 \text{ points}$
• $15 \text{ dollars} + s = 32 \text{ total dollars} \rightarrow 32 - 15 = 17 \text{ dollars}$
• $29 \text{ students} + 28 \text{ students} + 31 \text{ students} = 88 \text{ total students}$

Explanation

This is a get-together story! Parts are added to make a whole. If you know the total and one part, just subtract to find the missing piece. It's like solving a puzzle!

Property

starting amount - some went away = what is left ($s - a = l$)

Examples

• $20.00 \text{ dollars} - a = 15.17 \text{ dollars} \rightarrow 20.00 - 15.17 = 4.83 \text{ dollars}$
• $12 \text{ inches} - c = 8 \text{ inches} \rightarrow 12 - 8 = 4 \text{ inches}$
• $12 \text{ eggs} - 2 \text{ eggs} = 10 \text{ eggs left}$

Explanation

Imagine starting with something and a piece disappears! Subtraction finds what’s missing or what's left. To find the starting amount, add the missing piece back to what remains. It's like rewinding time!