Verified Solution • 2025–26 Session moderate

QJEEM20Mad58d: JEE Main 2020 Mathematics - Class 12 JEEM20Mad58d Solution: The probabilities of three events A, B and C are given by P(A)…

The probabilities of three events A, B and C are given by
P(A) = 0.6, P(B) = 0.4 and P(C) = 0.5.
If P(A ∪\cup B) = 0.8, P(A ∩\cap C) = 0.3, P(A ∩\cap B ∩\cap C) = 0.2, P(B ∩\cap C) = β\beta
and P(A ∪\cup B ∪\cup C) = α\alpha , where 0.85 ≤α≤\le \alpha \le 0.95, then β\beta lies in the interval :

Multiple Choice Options

  • A [0.35, 0.36]
  • B [0.20, 0.25]
  • C [0.25, 0.35]
  • D [0.36, 0.40]

Step-by-Step Verified Solution

P(A ∪\cup B) = P(A) + P(B) – P(A ∪\cup B)

⇒\Rightarrow 0.8 = 0.6 + 0.4 – P(A ∩\cap B)

⇒\Rightarrow P(A ∩\cap B) = 0.2

P(A ∪\cup B ∪\cup C) = P(A) + P(B) + P(C) – P(A ∩\cap B) – P(B ∩\cap C) –P(C ∩\cap A) + P(A ∩\cap B ∩\cap C)

⇒\Rightarrow α\alpha = 0.6 + 0.4 + 0.5 - 0.2 - β\beta - 0.3 + 0.2

⇒\Rightarrow α\alpha + β\beta = 1.2

⇒\Rightarrow α\alpha = 1.2 - β\beta

Given, 0.85 ≤α≤\le \alpha \le 0.95

⇒\Rightarrow 0.85 ≤\le 1.2 - β\beta ≤\le 0.95

⇒\Rightarrow 0.25 ≤β≤\le \beta \le 0.35

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