1969 AMC 12 Question 13 - thichhoctoan.com

Question 13

A circle with radius $r$ is contained within the region bounded by a circle with radius $R.$ The area bounded by the larger circle is $\frac{a}{b}$ times the area of the region outside the smaller circle and inside the larger circle. Then $R:r$ equals:

$\sqrt a:\sqrt b$
$\sqrt a:\sqrt{a-b}$
$\sqrt b:\sqrt{a-b}$
$a:\sqrt{a-b}$
$b:\sqrt{a-b}$