NCERT Class XI Mathematics - Probability - Solutions

Question : 38

Total: 54

If E and F are events such that P(E) =

, P (F) =

and P(E and F) =

, find (i) P(E or F), (ii) P(not E and not F).

Solution:

(i) P(E or F) = P(E ∪ F)
= P(E) + P(F) – P(E ∩ F) =

−

2+4−1

(ii) not E and not F = E′ ∩ F′ = (E ∪ F)′ (De Morgan’s Law)
\ P(not E and not F) = P(E ∪ F)′ = 1 - P (E ∪ F) = 1 -

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