Of the students attending a lecture , 50% could not see what was written on the board and 40% could not hear what the lecturer was saying. most unfortunate...30% fell into both of these categories. what is the probability that a student picked at random was able to see and hear satisfactorily? 

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May be let setA =not see =50% setB=not hear=40% set(A intersection B)=30% A union B=A+B-A intersection B =60% universal set -A union B=40% ans.
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