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?	Choose the correct choice:
A) 76.4%
B) 76.7%
C) 77.4%
D) 75%
E) 73.9%
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= 
<gadget id="calculator">70.2 + 6.5</gadget>
<output>76.7</output>
76.7%   ANS 76.7%
<result>B</result>
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?