Grade 4

Read the Headline Story to the class. Encourage them to use Cuisenaire^{©} Rods to create models that can be used to solve the problem.

Three sides of a triangle are whole-number lengths measured in centimeters. One side is 3 centimeters long and another side is 7 centimeters long. How many different lengths can the third side be?

- The third side cannot be shorter than 5 cm, because if it were 4 cm, the 3 cm and the 4 cm sides would fit flat against the 7 cm side and not make a triangle.
- The third side cannot be longer than 9 cm for a similar reason. So, 5 cm, 6, cm, 7 cm, 8 cm, and 9 cm lengths work. There are five possibilities.

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