This is tough. Is a mix of overlapping set and probability. However, once you have found the OS the rest is easy.

In my opinion, attacking the question using number is cumbersome.

Now, c stands for Clerks. a stands for Agents and x stands for both.

Total Clerks: c+x

Total Agents: a+x

Total: c+a+x

Divide in small chunks the question.

Of every three agents, one is also a clerk. means that an x employee which is part of both is over the agents category only \(\frac{x}{a+x}= \frac{1}{3}\) ;

a = 2xOf every two clerks, one is also an agent.\(\frac{x}{c+x} = \frac{1}{2}\) ;

c=xThe probability is

\(\frac{x}{c+a+x} = \frac{x}{x+2x+x} = \frac{x}{4x} = \frac{1}{4}\)

Hope this helps

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