Question

A rental car costs ​$ 30 per day plus ​$ 0.20 per mile. If someone has ​$ 250 to spend and needs to drive the car 60 miles each​ day, for how many days can that person rent the​ car? Assume that the car cannot be rented for part of a day.

Answer 1

so... for one day and no miles, the car costs 30*1, for 2 days 30*2, for 30*3 and so on, for "d" days, the car costs 30*d or 30d

now, if the driver drives it for 1 mile, the mileage costs is 0.20*1, for 2 miles is 0.20*2 for 3 miles is 0.20*3 and so on, for "m" miles, it costs 0.20*m or 0.2m

so, the actual costs to rent the car "d" days for "m" miles is really

C( d, m ) = 30d+0.20m

so.. if someone had only $250 to spend, and needs it for 60miles each day, how many days is that?  $\bf C( d, m ) = 30d+0.20m\qquad \begin{cases} C(d,m)=250\\ m=60 \end{cases}\\\\\\ 250=30d+0.20(60)$

solve for "d"