<PRE><B>Question 603164</B>
&quot;20 men can do a piece of work in 24 days.&quot; 
Find the number of man-days to complete the job
20 * 24 = 480 man-days
;
After working for six days an additional number of men is taken to finish the piece of work in 21 days from the beginning.
:
let a = no. of additional men 
(20*6) + 15(a+20) = 480
120 + 15a + 300 = 480
15a = 480 - 420
a = {{{60/15}}}
a = 4 additional men required to finish in 21 days
:
:
Check this
 120 + 15(24) = 480</PRE>