Factory X's bulbs work for over 5000 hours in 75% of cases, whereas factory Y's bulbs work for over 5000 hours in 65% of cases. It is known that factory X supplies 70% 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) 78%	C) 77.4%	D) 72%	E) 73.9%
For X, 70% of 75% will work.   For Y, 30% of 65% will work. *30% is the rest of the bulb supply in the market.   So, the probability that a purchased bulb will work is:   0.70(0.75) = .525   0.30(0.65) = 0.195   The combined probability then is 52.5 + 19.5= 
<gadget id="calculator">52.5 + 19.5</gadget>
<output>72</output>
72%   ANS 72%
<result>D</result>
Factory X's bulbs work for over 5000 hours in 75% of cases, whereas factory Y's bulbs work for over 5000 hours in 65% of cases. It is known that factory X supplies 70% of the total bulbs available. What is the chance that a purchased bulb will work for longer than 5000 hours?