Question 1204237
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Two mechanics worked on a car. The first mechanic charged 105 per hour, 
and the second mechanic charged 85 per hour. The mechanics worked for a combined total of 20 hours, 
and together they charged a total of 1800. How long did each mechanic work?
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<pre>
Let x = hours of the first mechanics; y = hours of the second mechanics.


Equations

       x +   y =   20      hours     (1)    combined time

    105x + 85y = 1800    dollars     (2)    combined dollars


To solve, express y = 20-x  from equation (1) and substitute it into equation (2).
You will get then


    105x + 85(20-x) = 1800

    105x + 1700 - 85y = 1800

    105x - 85y = 1800 - 1700

        20x    =     100

          x    =     100/20 = 5.


<U>ANSWER</U>.  First mechanics worked 5 hours; second mechanics worked 20-5 = 15 hours.


<U>CHECK</U>.   105*5 + 85*15 = 1800  dollars total combined.   ! correct !
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Solved.