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anne21 · Oct 28, 2007, 06:12 PM

Car A leaves Toronto for Montreal, 500km away, at an average speed of 80km/h. Car B leaves Montreal for Toronto on the same highway 2h later at 100 km/h. How far are they from Toronto when they pass?
I need a quadratic equation for this please.. tnx in advance. =D

galactus · Oct 29, 2007, 02:42 PM

Use d=rt. Then we have t=d/r.

Car A travels for d/80 hours and car B travels for (500-d)/100 hours.

Their difference is 2 hours.

$\frac{d}{80}-\frac{500-d}{100}=2$

Solve for d.

Another way to look at it is in terms of distance in terms of time:

car B travels 100(t-2) miles.

$100(t-2)=500-80t$

Solve for t, the amount of time driven. Then this can be plugged back in to find miles from Toronto.

terryg752 · Oct 29, 2007, 08:48 PM

Originally Posted by anne21

Car A leaves Toronto for Montreal, 500km away, at an average speed of 80km/h. Car B leaves Montreal for Toronto on the same highway 2h later at 100 km/h. How far are they from Toronto when they pass?
i need a quadratic equation for this please.. tnx in advance. =D

AN INTERESTING PROBLEM, IN THE SENSE THAT QUADRATIC EQUATION IS REALLY NOT NECESSARY!

Lets suppose they pass t hours after B starts

So B travels 100t

And A travels (t + 2) 80

Distance from Toronto:

500 - 100t = (t + 2) 80

You can find t from above

distance from toronto: 500 - 100t or (t +2) 80

math122 · Oct 12, 2011, 03:53 PM

h(t)=354-5t2+47t