A bag contains 2n+1 coins. It is known that n of these coins have a head on both sides where as the rest of the coins are fair. A coin is picked up at random form the bag and is tossed. If the probability that the results in a head is 3142, then the value of n is
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a
7
b
10
c
12
d
8
answer is B.
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Detailed Solution
Given, n coins have head on both sides and (n+1) coins are fair coins. Let E1= Event that an unfair coin is selected E2= Event that a fair coin is selected H= Event that the toss result in a head P(H)=PE1⋅PH/E1+PE2⋅PH/E23142=n2n+1⋅1+n+12n+1⋅12 ⇒ n=10