Final answer:
The radius of a circle with a diameter of 4.2 cm is 2.1 cm.
Step-by-step explanation:
The radius of a circle is half of its diameter, and the diameter is twice the radius. Therefore, if the circle has a diameter of 4.2 cm, its radius would be half of that, which is 2.1 cm. The diameter is the distance across the circle, while the radius is the distance from the center to any point on the circle.
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