Question

A bag contains n+1 coins. It is known that one of these

coins shows heads on both sides, whereas the other coins are fair. One coin is selected at random and tossed. If the

probability that toss results in heads is 7/12, then the value of

n is.

• A. 3
• B. 4
• C. 5
• D. None of these

Answer 1

Answer: (C)

5

Answer 2

Let , denote the event " a coin with two heads is selected and $E _ { 2 }$ , denote the event " a fair coin is selected". Let A be the even "the toss results in heads". Then,

and

∴

⇒ $[ \because \mathrm { P } ( \mathrm { A } ) = 7 / 12 ]$

⇒ $12 + 6 \mathrm { n } = 7 \mathrm { n } + 7 \Rightarrow \mathrm { n } = 5$