Solve the Problem $\frac { 1 } { 2 }$ B) $\frac { 1 } { 20 }$

Solve the problem.
-During a department store sale, 30 shoppers bought only clothing, 5 shoppers bought only towels, and 15 shoppers bought both clothing and towels. If 100 people shopped that day and a shopper is chosen at random, what is the probability that the shopper has bought towels?

A) $\frac { 1 } { 2 }$
B) $\frac { 1 } { 20 }$
C) $\frac { 1 } { 6 }$
D) $\frac { 1 } { 5 }$