Area of circle 1 = πr²
Area of circle 1 = π (10)²
Area of circle 1 = 100π km²
Area of circle 2 = πr²
Area of circle 2 = π (5)²
Area of circle 2 = 25π km²
Number of times the bigger circle is greater than the smaller circle

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Answer: The big circle is 4 times greater than the small circle.------------------------------------------------------------------------------------