Let A and B are two mutually exclusive events with  and  What is the value of 

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NDA (Held On: 23 April 2017) Maths Previous Year paper
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NDA 01/2025: English Subject Test
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Concept:

Mutually exclusive events:

  • Two events are said to be mutually exclusive if they cannot happen at the same time.
  • Example:  if we toss a coin, either heads or tails might turn up, but not heads and tails at the same time.
  • If A and B are mutually exclusive events then, P (A∩B) =0 and P (A ∪ B) = P (A) + P (B)


Complement of an event:

  • The complement of an event is the subset of outcomes in the sample space that are not in the event. A complement is itself an event.
  • The probability of the complement of an event is one minus the probability of the event.
  • P (A’) or P (Ac) or  = 1 - P (A) Where (A) be probability of Event A and P (A’) or P (Ac) or   be probability of the complement of Event A


Calculation:

Given: P(A) = 1/3 and P(B) = 1/4

As we know that 

Now, P(A ∪ B) = P(A) + P(B) – P(A ∩ B)

A and B are two mutually exclusive events so P(A ∩ B) = 0

∴ P(A ∪ B) = P(A) + P(B) = (1/3) + (1/4) = 7/12

Now,

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