A can do a work in 15 days and B in 20 days. If they work on it together for 6 days, then the fraction of the work that is left is  Choices.
A) 8/17 B) 7/15 C) 3/10 D) 8/15 E) 1/4
Person ( A ) ( B ) ( A+B )   Time - ( 15 ) ( 20 ) (-)   Rate - ( 20 ) ( 15 ) ( 35 )   Work -(300) (300) (300)   therefore A+B requires (300/35) days to complete entire work   For 1st 4 days they work  35 * 6= 
<gadget id="calculator"> 35 * 6</gadget>
<output>210</output>
210   Remaining work is 300 - 210= 
<gadget id="calculator">300 - 210</gadget>
<output>90</output>
90   Remaining fraction of work is= 90/300 = 3/10   Answer 3/10
<result>C</result>
A can do a work in 15 days and B in 20 days. If they work on it together for 6 days, then the fraction of the work that is left is