Question 1185447
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Let x be the number of students (the entire audience).


Then from the condition


    0.4x - 0.3x = 18.


or


       0.1x    = 18.


Hence,


          x    = 18/0.1 = 180.


<U>ANSWER</U>.  The question is  "How many were at the seminar", but it does not specify "how many of whom".


         The entire audience was 180 people, in all.
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