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 %

Rationale: "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 = 72 % ans d"
Answer: D