A tank has 5 inlet pipes. Three pipes are narrow and two are wide. Each of the three narrow pipes works at 1/2 the rate of each of the wide pipes. All the pipes working together will take what fraction K of time taken by the two wide pipes working together to fill the tank?	Select:
A) 1/2	B) 2/3	C) 3/4	D) 3/7	E) 4/7
I always plug in for these questions.. I find them easier   Let 2 large pipes each work fill 10lts/hr   small ones = 1/2*10= 
<gadget id="calculator">1/2*10</gadget>
<output>5</output>
5   total 5= 10+10+5+5+5= 
<gadget id="calculator">10+10+5+5+5</gadget>
<output>35</output>
35 lts/hrs   now assume the total capacity= 140 lts ( LCM of 20,35)   Qn :All the pipes working together will take what fraction of time taken by the two wide pipes working together to fill the tank   all working together will take 140/35= 
<gadget id="calculator">140/35</gadget>
<output>4</output>
4 hrs   two large pipes working will take   140/20= 
<gadget id="calculator">  140/20</gadget>
<output>7</output>
7 hrs   hence ratio K= 4/7 = 4/7
<result>E</result>
A tank has 5 inlet pipes. Three pipes are narrow and two are wide. Each of the three narrow pipes works at 1/2 the rate of each of the wide pipes. All the pipes working together will take what fraction K of time taken by the two wide pipes working together to fill the tank?