# Lesson 4 Change Unknown Story Problems

Let’s solve story problems.

## Warm-up How Many Do You See: Numbers to 20

How many do you see?

How do you see them?

## Activity 1 Field Trip to the Aquarium

Solve each problem.

Show your thinking using drawings, numbers, or words.

Clare saw 8 sea turtles swimming together in the tank.

Some more turtles joined them.

Now there are 15 turtles in the tank.

How many turtles joined the group?There were 17 penguins sitting on the rocks.

Some of the penguins went back into the water.

Now there are 5 penguins sitting on the rocks.

How many penguins went back into the water?The seal trainer brought out a bucket of 20 fish to feed to the seals.

The seals ate some of the fish.

Now there are 3 fish left in the bucket.

How many fish did the seals eat?In the touch pools, Tyler felt 6 stingrays.

Then he felt some sea stars.

Tyler felt 14 animals all together.

How many sea stars did Tyler feel?

## Activity 2 Find the Unknown Number

Clare watched 16 bullfrogs at the aquarium.

Then some of them swam away.

Now Clare can only see 9 bullfrogs.

How many bullfrogs swam away?

Andre wrote

Show Andre how you would find the unknown number.

Show your thinking using drawings, numbers, or words.