# Thread: Simple functions problem

1. ## Simple functions problem

Please help with this question: The speed r (in mph) to which a car can accelerate in t seconds can be described by r(t) = -0.15t^2 + 6.75t + 13.75, 0 < t < 25. How long does it take the car to accelerate to 60 mph?

I'm not certain if I solved this correctly, but I set up the equation as
60 = -0.15t^2 + 6.75t + 13.75, and ended up with t = 8.432 and t = 36.568 when I solved it as a quadratic. If this is correct, would both solutions be answers to this problem?

2. Originally Posted by currypuff
Please help with this question: The speed r (in mph) to which a car can accelerate in t seconds can be described by r(t) = -0.15t^2 + 6.75t + 13.75, 0 < t < 25. How long does it take the car to accelerate to 60 mph?

I'm not certain if I solved this correctly, but I set up the equation as
60 = -0.15t^2 + 6.75t + 13.75, and ended up with t = 8.432 and t = 36.568 when I solved it as a quadratic. If this is correct, would both solutions be answers to this problem?
Yes, both answers are correct. An easy way to check your answers are to plug them back into the formula. If you did it properly, you will get the results you expect (meaning 60)