This is a sample question for middle school math, published by the International Baccalaureate (IB) program. I found it here.
Looking at this graph, you see that after about 10 minutes, there are 11 cars per minute going through the intersection – and that’s the most cars. After about 25 minutes, there are zero cars going through the intersection, and after that, there is a negative number of cars (!!!).
I don’t think this equation models anything having to do with any intersection I’ve ever visited. Instead, I think that any intersection controlled by a traffic light is going to be more periodic, that is to say, something like some mix of sine or cosine functions — obviously not middle school material.
Guy's Math & Astro Blog 
That’s a reasonable question for a very good middle school student. Most won’t have a clue. At least in the U.S. Which is sad.
As to how ‘correct’ the question is, vis a vis, your stoplight comment, it does seem suspect. As a teaching question, it’s ok, but should not be on an exam.
Bart
*Sic itur ad astra!*
On Tue, Jul 20, 2021 at 10:35 AM Guy’s Math & Astro Blog wrote:
> gfbrandenburg posted: ” This is a sample question for middle school math, > published by the International Baccalaureate (IB) program. I found it here. > Here is a graph I made of this equation, using Desmos: Looking at this > graph, you see that after about 10 minutes, th” >
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I agree, the average middle schooler who has never learned about parabolas probably won’t have a clue. Frankly, I’m not even sure what this problem is supposed to teach or what skills or knowledge it is trying to test. If a person is in fact going to go to the trouble of seriously creating >>by hand<< a table and then a graph, by 10-second intervals (which would make sense at an intersection in one of the largest cities in the Western Hemisphere), then it would require a huge amount of time. And then to discover that it takes 20 minutes for the intersection to clear?
Such an exercise would teach kids that math has, in fact, nothing to do with the real world.
Which is the exact opposite of what I would like to show.
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