factory x ' s bulbs work for over 5000 hours in 78 % of cases , whereas factory y ' s bulbs work for over 5000 hours in 65 % of cases . it is known that factory x supplies 90 % of the total bulbs available . what is the chance that a purchased bulb will work for longer than 5000 hours ?
"for x , 90 % of 78 % will work . for y , 10 % of 65 % will work . * 10 % is the rest of the bulb supply in the market . so , the probability that a purchased bulb will work is : 0.90 ( 0.78 ) = . 702 0.10 ( 0.65 ) = 0.065 the combined probability then is 70.2 + 6.5 = 76.7 % ans b"
divide(add(78, 65), const_2)