<PRE><B>Question 248883</B>
A can finish 1/24th of the task in 1 hr

B can finish 1/40th of the task in 1 hr

Let 1 denote the full task

Then (1/24 + 1/40)(t)=1, where t denotes the time spent working together

Multiply by the LCM:

(5+3)t=120

8t=120

t=15 hr (Answer) </PRE>