BITSAT 2014 Paper

Let E1 denote the event "a coin with head on both sides is selected" and E2 denotes the event " a fair coin is selected". Let A be the event " he toss, results in heads".
∴ P(E1) =

1

n+1

, P(E2) =

n

n+1

and P(

A

E1

) = 1 , P(

A

E2

) =

1

2

∴ P (A) = P(E1) P (

A

E1

) + P(E2)(

A

E2

)
⇒

7

12

=

1

n+1

× 1 +

n

n+1

×

1

2

⇒ 14n + 14 = 24 + 12n ⇒ n = 5