SEAMO 2017 — Paper E — Grade 9–10 Question 18

Question 18

A small circle with radius $r$ and centre $D$ is tangent to three identical semicircles with centres $A,B,C$ and radius $R$ as shown. Find $R:r$.

Question illustration

$2:1$
$3:1$
$5:2$
$7:5$
None of the above