4 Three circles of radius 20 are arranged with their respective centres $A, B$ and $C$ in a row. If the line $W Z$ is tangent to the third circle, find the length of $X Y$.
(A) 30
(B) 32
(C) 34
(D) 36
(E) 38
4 Answer: (B)
Let $P$ be the midpoint of $X Y$ and $Q$ be the point where the line $W Z$ meets the third circle.

Then by similar $\Delta \mathrm{s}, \frac{P B}{60}=\frac{20}{100} \Rightarrow P B=12$. Hence $X Y=2 X P=2 \sqrt{20^{2}-12^{2}}=32$.