Task: Question Answering
Input (English): Problem: factory x ' s bulbs work for over 5000 hours in 79 % of cases , whereas factory y ' s bulbs work for over 5000 hours in 85 % of cases . it is known that factory x supplies 80 % of the total bulbs available . what is the chance that a purchased bulb will work for longer than 5000 hours ? 
Options: a ) 80.2 % , b ) 88 % , c ) 87.4 % , d ) 85 % , e ) 83.9 %
Output (English): a