Question

Two mechanics worked on a car. The first mechanic worked for 10 hours, and the second mechanic worked for 5 hours. Together they charged a total of $725. What was the rate charged per hour by each mechanic if the sun of the two rates was $100 per hour?

Answer 1

You have two unknown rates, so we need to develop two equations to solve for these unknowns (based on the information given on the problem statement):

5x + 10y = 725
x + y = 100

By substitution, we get:

5x + 10(100 - x) = 725
5x + 1000 - 10x = 725
-5x = 725 - 1000
-5x = -275
x = -275/-5 = 55

100 - 55 = 45

Thus:
The mechanic who worked for 5 hours charged his time at $55/hr, and the mechanic who worked for 10 hours charged his time at $45/hr.

To verify, plug and chug the results back into the original equations:

5(55) + 10(45) = 725
275 + 450 = 725
725 = 725 [OK]

55 + 45 = 100 [OK]