8 coins are tossed. Whats is the probability that one and only one turns up head ?  Choose the correct choice from the following options.
A) 1 / 256
B) 1 / 32
C) 1 / 64
D) 1 / 128
E) 1 / 189

Rationale: explanation : possible outcomes ( sample space ) when 8 coins are tossed are : ( h , h , h , h , h , h , h , h ) , ( h , h , h , h , h , h , h , t ) , ( h , h , h , h , h , h , t , h ) , ( h , h , h , h , h , h , t , t ) , . . . . . . . ( t , t , t , t , t , t , t , t ) = 28 required outcomes : ( h , t , t , t , t , t , t , t ) , ( t , h , t , t , t , t , t , t ) , ( t , t , h , t , t , t , t , t ) , ( t , t , t , h , t , t , t , t ) , ( t , t , t , t , h , t , t , t ) , ( t , t , t , t , t , h , t , t ) , ( t , t , t , t , t , t , h , t ) , ( t , t , t , t , t , t , t , h ) = 8 so the required probability = 8 / 28 = 1 / 32 answer : b
Answer: B