A plumber charges $75 for the first 30 minutes of each house call plus $2 for each additional minute that she works. The plumber charges Adam $113 for her time. For what amount of time, in minutes, did the plumber work?

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Answer 1 · 2016-08-10T09:23:08

49 minutes

We can construct a formula for the plumber's fee.

#C = color(red)(75) + color(blue)(2n)#

The red 75 denotes the $75 that is charged for the first half hour. #n# is the number of minutes over that that she works.

Cost is $113 so

#113 = 75 + 2n#

Can subtract 75 from both sides of the equation without changing anything about it:

#113-75 = 38 = 2n#

Divide both sides by 2:

#19 = n#

She worked 19 minutes over the first 30, so worked #19+30 = 49# minutes in total.