Grade
2

How Many Are Hidden? Cube Trains

The number of cubes in both pictures is the same.

How many cubes are hidden behind the cloud? How do you know?
How can you finish the equation to make it true?

The picture on the left shows 2 trains of 10 blue Unifix cubes and 8 single red cubes. The picture on the right shows 1 train of 10 blue Unifix cubes and 5 single cubes. A cloud covers an unknown number of red cubes. Blue 20 + red 8 = blue 15 + red blank.

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

In the equation blue 20 + red 8 = blue 15 + red blank, the 20 changes to 15. How does the 8 change if the equation is true?
  • Now there are more than 28 cubes. You get to decide how many!
    How many could be hidden behind each cloud? How do you know?
  • Complete the equation to make it true.
    What do you notice about how the numbers changed?
The picture on the left shows 2 trains of 10 blue Unifix cubes and a cloud hiding an unknown number of red cubes. The picture on the right shows 2 trains of 10 blue Unifix cubes and 2 single cubes. A cloud hides an unknown number of red cubes. Blue 20 + red blank = blue 22 + red blank.
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