Be a Math Detective!

Lesson Plan - Get It!

Audio:

Your mission is to solve for missing numbers in special number sentences. Think of these as fun puzzles where something is missing. That's where your detective skills come in! Ready to try it out?

Case 1: The Dog Stickers

Imagine you have 10 dog stickers. Your friend gives you some more. Now you have 15 dog stickers.

• How many stickers did your friend give you?

Use your detective skills to figure it out! Here’s the number sentence.

10 + ? = 15

Start with 10 and count up to 15.

10... 11, 12, 13, 14, 15

• What did you find?

10 + 5 = 15

Your friend gave you 5 stickers! Great job!

When you solve an addition problem, you must add a number plus another number to find the total. The numbers you add together to find the total are called addends.

Sometimes, an addend is missing. That's when you must be a number detective and figure out the missing number!

Try solving another case!

Case 2: The Duck Pond

6 yellow ducks are swimming in the pond. Then, some white ducks join them. Now, there are 9 ducks.

• How many white ducks came to the pond?

Use this number sentence.

6 + ? = 9

You can draw a part-part-whole bar model like the one below to see how the parts fit together.

• What addend do you need to make the 6 into 9?

Take a moment to think! You got it!

You did a great job finding the missing addend!

Sometimes, when you subtract, a number is missing. This missing number is called a subtrahend.

You can be a math detective to find the missing subtrahend.

• Are you ready to give it a try?

Case 3: The Cookie Conundrum

You start with 12 cookies. You decide to share a few. Now, you have 8 cookies left.

• How many cookies did you share?

You started with 12, and you gave away some. When you give something away, you have to subtract.

So, this time, use a subtraction number sentence.

12 - ? = 8

A picture can help you find the missing subtrahend.

Draw 12 circles and cross out some until you have 8 left. Take a look.

• How many circles did you cross out?

You crossed out 4.

12 - 4 = 8

Way to go, math detective!

You did an amazing job finding the missing numbers! Now, watch this video to learn even more ways to solve for missing addends and subtrahends.

• Are you ready for more?

Great job! Now you know even more ways to solve for missing numbers.

Now that you're a math detective try another mystery!

• How did you do?

Great job being a math detective!