A can do a piece of work in 20days, and B can do it in 15days. How long will they take if both work together?  Choose the correct answer: A) 7days B) 8.6days C) 13days D) 5.6days E) 10days
A+8.6days can do the work in 20*15 / 20+15 = 20*15/35 = 8.6days   Answer is 8.6days
<result>B</result>
A can do a piece of work in 20days, and B can do it in 15days. How long will they take if both work together?