Two circles are tangent to each other externally. The radius of the first circle is 5 units, and the radius of the second circle is 3 units. What is the distance between their centers?
Correct: C
When two circles are tangent externally, the distance between their centers is equal to the sum of their radii.
Let r1 be the radius of the first circle and r2 be the radius of the second circle.
r1 = 5 units
r2 = 3 units
Distance between centers = r1 + r2 = 5 + 3 = 8 units.