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7
Q:

A fair coin is tossed 11 times. What is the probability that only the first two tosses will yield heads ?

A) (1/2)^11 B) (9)(1/2)
C) (11C2)(1/2)^9 D) (1/2)

Answer:   A) (1/2)^11



Explanation:

Probability of occurrence of an event, 

P(E) = Number of favorable outcomes/Numeber of possible outcomes = n(E)/n(S)


⇒ Probability of getting head in one coin = ½, 

⇒ Probability of not getting head in one coin = 1- ½ = ½, 

Hence, 

All the 11 tosses are independent of each other.

∴ Required probability of getting only 2 times heads =122×129=1211

Subject: Probability
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