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How Many Are Hidden? Ice Skates

The number of ice skates in both pictures is the same.

How many skates are hidden behind the door? How do you know?

How can you finish the equation to make it true?

On the left: 7 blue ice skates and 6 red ice skates. On the right: 10 blue ice skates and an unknown number of red skates behind a door. 7 + 6 = 10 + blank.

What do you notice about how the blue number changed? What about the red number?

Blue 7 + red 6 = blue 10 + red blank. Notice that the blue number changed from 7 to 10.
  • Now there are more than 13 ice skates in both pictures. You get to decide how many!
    How many ice skates could be hidden behind each door? How do you know?
  • Complete the equation to make it true.
    What do you notice about how the numbers changed?
On the left, 10 blue ice skates and an unknown number of red skates behind a door. On the right, 7 blue skates and an unknown number of red skates behind a door. Blue 10 + red blank = blue 7 + red blank.
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