<PRE><B>Question 1152573</B>
Four workers are building a house.
 In five days they built half the house. 
But winter is coming and they want to finish building the house in two more days.
How many friends should the workers call for help, if they do not want to bother
more people than is necessary?
:
Find how many man-days to complete a house 
2(4*5) = 40 man-days
:
let m = no. of additional men required to complete in 2 days
(20 man-days to complete 1st half the house)
20 + 2(m+4) = 40
2m + 8 = 40 - 20
2m = 20 - 8
2m = 12
m = 6 more men required</PRE>