X is three times as fast as Y and working together, they can complete a work in 20 days. In how many days can Y alone complete the work?  Options:
A) 11 days  B) 80 days  C) 13 days  D) 15 days  E) 19 days
X = 3Y   X + Y = 3Y + Y = 4Y   These 4Y people together can do the work in 20 days, which means Y can alone do the work in  4*20= 
<gadget id="calculator"> 4*20</gadget>
<output>80</output>
80 days.   Answer : 80 days
<result>B</result>
X is three times as fast as Y and working together, they can complete a work in 20 days. In how many days can Y alone complete the work?