Question

A plumber and his assistant work together to replace the pipes in an old house. the plumber charges $35 an hour for his own labor and $20 an hour for his assistant's labor. the plumber works twice as long as his assistant on this job, and the labor charge on the final bill is $1800. how long did the plumber and his assistant work on this job?

Answer 1

X= plumber's hours
y= assistant's hours
x=2y (because plumber works twice as long as assistant)

35x+20y=1800
Substitute x=2y
35(2y)+20y=1800
70y+20y=1800
90y=1800
Divide both sides by 90
y=20 assistant's hours

x= 2y
2(20)= 40 plumber's hours

Check:
35x+20y=1800
35(40)+20(20)=1800
1400+400=1800
1800=1800

Hope this helps! :)