Here is the problem I am having trouble with right now.(adsbygoogle = window.adsbygoogle || []).push({});

The number of miles M that a certain compact car can travel on 1 gallon of gasoline is related to its speed v (in mi/hr) by

M=-1/30v^2+5/2v for 0<v<70

For what sppeds will M be at least 45?

I start working the problem like this:

45=-1/30v^2 +5/2v

I then put the problem into a polynomial

-1/30v^2 + 5/2v -45

I'm fairly certain you can factor that but if not I use the quadratic.

-5/2 +- Sqr of .25 all over -1/15

That comes out to be 75/2 plus or .5

Which is equal to 38 and 37

Now three things are possible. a) I am heading in the wrong direction or b)I did something wrong or c)all the above

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# Homework Help: Inqualities with gas mileage

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