The perimeter of an equilateral triangle is 18900 mm. What is the length of its side in decimetres?

1. Since the perimeter of a triangle is equal to the sum of the three sides of this triangle, and this triangle is equilateral, that is, all its sides are equal, we define what is the length of one side of this triangle.
18900/3 = 6300 millimeters.
2. Since one decimeter is equal to one hundred millimeters, then 6300 millimeters will be equal to 6300/100 = 63 decimeters.
Answer: The length of one side of an equilateral triangle is sixty-three decimeters.

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