I am not sure if my method is correct, but here's how I think you should approach this problem:
Total number of people = 248
Number of married people = 156
Number of self employed people = 70
Number of people who are married AND self employed = 25% of 156 = 39
Number of people who are self employed but not married = People self employed - People self employed/married
Thus, number of people who are self employed but not married = 70-39 = 31
Thus probability = 31/248 = 1/8
Does this match the correct answer specified?
Also, I've attached a diagrammatic view of how this might work.
@Others: Please let me know if my approach is right!
Attachments
File comment: Venn Diagram Version of Problem

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