Let E and F be two independent events. The probability that exactly one of them occurs is 1125 and the probability of none of them occurring is 225. If P(T) denotes the probability of occurrence of the event T, then
A
P(E)=45,P(F)=35
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B
P(E)=15,P(F)=25
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C
P(E)=25,P(F)=15
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D
P(E)=35,P(F)=45
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Solution
The correct options are AP(E)=45,P(F)=35 DP(E)=35,P(F)=45
P(E∪F)−P(E∩F)=1125 . . . (i) [i.e. only E or only F]
Probability that neither of them occurs =225 ⇒P(¯E∩¯F)=225⋯(ii) From Eq. (i), P(E)+P(F)−2P(E∩F)=1125 . . . (iii) From Eq. (ii), (1−P(E))(1−P(F))=225 ⇒1−P(E)−P(F)+P(E).P(F)=225 . . .(iv) From Eqs. (iii) and (iv), P(E)+P(F)=75andP(E).P(F)=1225∴P(E).[75−P(E)]=1225⇒(P(E))2−75P(E)+1225=0⇒[P(E)−35][P(E)−45]=0∴P(E)=35or45⇒P(F)=45or35