X and Y can do a piece of work in 20 days and 12 days respectively. X started the work alone and then after 4 days Y joined him till the completion of work. How long did the work last?  Choose the correct choice: A) 8 days B) 10 days C) 12 days D) 13 days E) 14 days
Let the total units of work to be completed be 60.   Units of work completed by X in a single day = 60/20= 
<gadget id="calculator">60/20</gadget>
<output>3</output>
3 units.   Units of work completed by Y in a single day= 60/12= 
<gadget id="calculator">60/12</gadget>
<output>5</output>
5 units.   Thus, 8 units of work can be done by them in a single day working together.   X works for 4 days alone= 12 units of work.   Remaining work = (60 - 12)= 
<gadget id="calculator">(60 - 12)</gadget>
<output>48</output>
48 units.   Now, X and Y works together to complete the remaining work= 48/8= 
<gadget id="calculator">48/8</gadget>
<output>6</output>
6 days   Hence, total days taken to complete the work= (6 + 4)= 
<gadget id="calculator">(6 + 4)</gadget>
<output>10</output>
10 days.   ANSWER:10 days
<result>B</result>
X and Y can do a piece of work in 20 days and 12 days respectively. X started the work alone and then after 4 days Y joined him till the completion of work. How long did the work last?