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 Question from Theresa: I have a job that is $25,250 total to complete the job. The custome asked how muck am I charging. I told him I was charging 15% over the Cost. What is the formula to culcaulate the cost of the job. I do not know the cost at all I just gave him a number ($25,250) I am not sure what formula to use to culcate cost of the job???? Help thanks

Hi Theresa.

Let's use algebra to solve the problem.

Let C = the cost. Then 15% of C is your surcharge. When you add these together, you get $25,250. Remember that percentages can be written as decimals. 15% = 0.15. So we can write the question as follows: C + (0.15 C) =$25250

We want to "solve for C" so we have to simplify:

1 C + 0.15 C = $25250 (1 + 0.15) C =$25250
1.15 C = $25250 Then to isolate C on the left side of the equal sign, we divide both sides by 1.15: 1.15 C 1.15 =$25250 1.15
C = $25250 1.15 C =$21956.52

And this is the answer. Your cost is expected to be $21956.52, your surchange (perhaps this is your labour charge and the cost is your materials charge) is$3293.48 (that's 15% of $21956.52) for a total of$25250.

Hope this helps,
Stephen La Rocque.

Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences.