A tank is fitted with 8 pipes, some of them that fill the tank and others that are waste pipe meant to empty the tank. Each of the pipes that fill the tank can fill it in 8 hours, while each of those that empty the tank can empty it in 6 hours. If all the pipes are kept open when the tank is full, it will take exactly 6 hours for the tank to empty. How many of these are fill pipes?	Answers: A) 1 B) 2 C) 3 D) 4 E) 5
X PIPES FILL AN4 8-X EMPTY   IN 1hr 1/6th is emptied so :   x/6 - (8-x)/8 = 1/6   ON SOLVING X=4 (FILL PIPES) AN4 8-X=4(EMPTY PIPES)   ANSWER:4
<result>D</result>
A tank is fitted with 8 pipes, some of them that fill the tank and others that are waste pipe meant to empty the tank. Each of the pipes that fill the tank can fill it in 8 hours, while each of those that empty the tank can empty it in 6 hours. If all the pipes are kept open when the tank is full, it will take exactly 6 hours for the tank to empty. How many of these are fill pipes?