Question 582880
A bricklayer lays an average of 150 bricks per hour.
 During a job, he is called away and replaced by a less experienced man, who averages 120 bricks per hour.
 The two men laid 930 bricks in 7 hours. How long did each work?
:
Let x = time worked by the experienced bricklayer
Let y = time worked by apprentice 
:
Time equation
x + y = 7
y = (7-x); use this form for substitution
:
Production equation
150x + 120y = 930
replace y with (7-x), find x
150x + 120(7-x) = 930
150x + 840 - 120x = 930
150x - 120x = 930 - 840
30x = 90
x = 90/30
x = 3 hrs worked the exp guy
:
You can find the hrs worked by the other guy. check solutions in the production equation