How solve it?

Camila begins to exercise in a new gym where the coach explains that the work consisted in 5 minutes of warm-up 25 trot and 15 days in the eliptca machine .... at the end of each week of training should increase 3 minutes of jogging and 5 of elliptical machine in how many weeks will the trotting time be equal to the time that camila uses the elliptical machine?

A) 5
B) 4
C) 6
D) 7


1 Answer
Jun 3, 2017

After 5 weeks.


I'm assuming that the elliptical workout time is 15 mins and not 15 days (cause that's a looong time).
You need to set up two equations. They will be of the form, time of each workout (t) as a function of number of weeks (x).

The trotting time starts off as 25 mins, then increases by 3 mins per week. In other words, 25 + 3 times the number of weeks. So the equation looks like this:


In the same way, the time of the elliptical machine is 15 mins plus 5 mins per week:


To solve for #x#, set the times equal to each other:


Then solve for #x#:





The workout time will be given by substituting the answer for #x# into each equation.
You can see the answer by graphing the two straight lines and seeing where they intersect (5,40):
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