SOLUTION: In a certain city of 15000 families, 3.5% of families who read A but not B look into advertisement, 25% of families who read B but not A look into advertisement and 50% of families

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Question 1126125: In a certain city of 15000 families, 3.5% of families who read A but not B look into advertisement, 25% of families who read B but not A look into advertisement and 50% of families who read A and B look into advertisement. It is known that 8000 families read A, 4000 read B and 1000 both A and B.
Find the number of families who look into advertisements.
Answer by ikleyn(52779) About Me  (Show Source):
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From the condition,


    the set  (A n B)  ("A intersection B")  of those who read both A and B is 1000 families;

    the set  (A \ (A n B)) of those who read A but not B is 8000-1000 = 7000 families;

    the set  (B \ (A n B)) of those who read B but not A is 4000-1000 = 3000 families.



Thus the number of families who look into advertisements is


    0.035*7000 + 0.25*3000 + 0.5*1000 = 1495  families.



Answer.  The number of families who look into advertisements is  1495.

Solved.