Unit 8 — Solving Addition and Subtraction Problems

Welcome back!

Now that you understand both addition and subtraction, it is time to use them together.

Good mathematicians first understand the problem.

Then they decide which operation to use.

Finally, they check whether the answer makes sense.

Read Carefully

Before solving a problem:

1. Read it slowly.
2. Read it again.
3. Think about what is happening.
4. Decide whether you should add or subtract.

Taking a little extra time often helps you find the correct answer.

When Do We Add?

Addition usually means:

• putting groups together
• getting more
• combining
• joining

Example:

Sofia has 5 books.

Her grandmother gives her 4 more books.

How many books does Sofia have now?

5 + 4 = 9

Sofia now has 9 books.

When Do We Subtract?

Subtraction usually means:

• taking away
• finding what remains
• finding the difference
• having fewer

Example:

Noah has 9 balloons.

One balloon pops.

How many balloons are left?

9 − 1 = 8

Noah has 8 balloons remaining.

Looking for Clues

Certain words can help.

Words that often mean add:

• together
• in all
• total
• altogether
• more
• combine

Words that often mean subtract:

• left
• remain
• fewer
• take away
• difference

These words are clues, but always think about the whole story.

Draw a Picture

Pictures often make problems easier.

If Mia has 6 flowers and picks 2 more, you might draw:

🌸🌸🌸🌸🌸🌸

+

🌸🌸

Now count them all.

Pictures help us understand what the numbers mean.

Check Your Answer

After solving, ask yourself:

Does my answer make sense?

Could I solve it another way?

Did I read the question carefully?

Great mathematicians always check their work.

Activity

Create your own story problem.

It can be about:

• pets
• toys
• fruit
• books
• friends

Write the story.

Write the number sentence.

Solve it.

Ask someone else to solve your problem too.

Practice

Solve these problems.

Emma has 7 apples.

Her father gives her 2 more.

How many apples does she have?

Jack has 10 toy cars.

He gives 3 to his brother.

How many cars does Jack have now?

Lily has 4 blue balloons and 5 red balloons.

How many balloons does she have altogether?

There are 8 birds in a tree.

2 fly away.

How many birds remain?

Review

Today you learned:

• how to choose between addition and subtraction
• how clue words can help
• why drawing pictures is useful
• why checking your answer is important
• that good mathematicians think carefully before solving problems

Every problem tells a story.

Understanding the story helps you choose the correct mathematics.

Looking Ahead

Next we will explore measurement.

You will learn how to compare:

• length
• height
• weight
• capacity

Mathematics helps us measure the world around us.