Missing Addend Detective

Lesson Plan - Get It!

Audio:

Addition problems involve adding together "some number" and "some number" to find the total.

For example, Jerry had 15 movies and bought 5 more movies.

• How many does he have now?

Add 15 + 5 to get a total of 20 movies.

Sometimes, addition story problems give us the total and an addend is missing. An addend is a number that is added to another number. In order to solve these types of problems, subtract to find the missing number.

Watch a short Teaching Without Frills video about solving for the missing addend. As you watch Missing Addends: Finding a Missing Part for Kids, pay attention to how they use a model to solve for the missing addend:

Then, after the video, discuss with an adult or teacher how to find the missing addend in an addition problem.

Now, learn to use the part-part-whole model to figure out the missing addend in the question you read at the beginning of the lesson.

Sammy had 13 toy cars on the table, but now he only has 5. How many cars are missing?

• What is the whole amount?

13, so that goes at the top of our model.

• What is a part of that amount?

5, so that goes on the bottom of our model.

• What is the missing part, or addend?

5 + ? = 13

To solve for this problem, think of what number plus 5 will equal 13. Or use the inverse operation of addition, which is subtraction.

Some numbers are easier to subtract in your mind, but other times the numbers will be too large and you will need to use subtraction.

13 - 5 = 8.

Be sure to check your answer.

• Does 5 + 8 = 13?

Yes! There are 8 cars missing.

Take a look at another example:

In the first half of the basketball game, Tina scored 17 points. In the whole game, she scored 35 points.

• How many points did Tina score in the second half?

• What is the whole amount?

35 points

• What is a part of that amount?

17 points (from the first half)

• What is the missing part, or addend?

17 + ? = 35

Find the unknown addend by subtracting the known addend, 17, from the sum, which is 35.

Since 35 - 17 = 18, we find that Tina scored 18 points in the second half. Don't forget to check your answer.

• Does 17 + 18 = 35?

Yes!

• What if you have to find the missing addend in a problem with time or weather?

The steps are the same!

The temperature at noon was 55 degrees, which was 19 degrees warmer than what it was at 7am.

• What was the temperature at 7am?

Think of the problem, 19 + ? = 55. In order to find the missing addend, subtract the total, 55, from the addend, 19. 55 - 19 = 36. It was 36 degrees at 7am! Brrrr!

Discuss with an adult or teacher:

• How do you use the part-part-whole model to help you find the missing addend?
• How do we check our problem after we have found a solution?
• What information in the problem helps us find the missing addend?

Missing addends can be found by first setting up a model and then subtracting. Keep that in mind and go on to the Got It? section to practice with interactives!