<PRE><B>Question 877485</B>
The total number of workers in a factory is 120, and they earn an average wage of $80 per month.
Some of them earn a wage of $60 and all of the rest earn a wage of $90.Find the number of workers who earn a wage of $60?
:
Let x = no. of workers that earn $60
then
(120-x) = no. of workers that earn $90
:
{{{(90(120-x) + 60x)/120 = 80}}}
multiply both sides by 80
90(120-x) + 60x = 80(120) 
10800 - 90x + 60x = 9600
-90x + 60x = 9600 - 10800
-30x = -1200
x = -1200/-30
x = +40 workers earn $60
:
:
Check this
80*90 = 7200
40*60 = 2400
--------------
total: 9600
av = 9600/120 = 80</PRE>