question_answer

Two light bulbs are connected in series in a circuit. The probability that an increase in voltage above its rated value will break the circuit if, under these assumptions, the chance that a bulb bums out is \[0.4\] for each of the two bulbs, is

A) \[0.64\]        

B)                                    \[0.48\]

C) \[0.16\]               

D)    \[0.8\]

Correct Answer: A

Solution :

P (bulb burns) = 0.4                 Hence P (circuit breaks = P (A burns and B does not) + P (A does not burn and B burns) = (0.4) (1) + (0.6) (0.4) (If A burns circuit breaks) = 0.4 + 0.24 = 0.64