<PRE><B>Question 963815</B>
A garrison of 400 men had food enough for 15 weeks.
They had: 400*15 = 6000 man-weeks of food
:
 Some men were sent out and the food lasted for 20 weeks.
 How many men were sent out?
let m = no. of men sent out
20(400-m) = 6000
8000 - 20m = 6000
-20m = 6000 - 8000
-20m = -2000
m = -2000/-20
m = +100 men sent out
:
:
Confirm this. 400 - 100 = 300 men actually
300 * 20 = 6000 man-weeks</PRE>