Qa 03

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course MTH 173

10:40 6/13

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Question: `q001. Sketch a graph similar to that you constructed for the stock values, this time for the depth of the water vs. clock time (depths 80, 40, 20 at clock times 10, 40, 90). Your first point, for example, will be (10, 80). Connect these points with straight lines and determine the slopes of the lines.

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Your solution:

(y2-y1)/(x2-x1)

(40-80)/(40-10)= -40/30 or -1.33 line one

(y2-y1)/(x2-x1)

(20-40)/(90-40)= -20/50 or -.4 line two

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Given Solution:

`aThe three points are (10, 80), (40, 40) and (90, 20).

From the first point to the second the rise is from 80 to 40, or -40, and the run is from 10 to 40, or 30. So the slope is -40 / 30 = -1.33.

From the second point to the third the rise is from 40 to 20, or -20, and the run is from 40 to 90, or 50, so the slope is -20 / 50 = -.4. Click on 'Next Picture' to see graph.

`routine graph3

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Question: `q002. Look at your results for the slopes, and look the results for the average rates of change. What do you notice? In what way then does the graph represent the average rate of change?

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Your solution:

The slope of the graph is the average rate of change so they are both equivalent to one another. I’m not sure what the depth is measured in for this problem nor do I know the time (I’m assuming its in the picture of the graph but I couldn’t find the link) but I will use meters and seconds.

Ex: The first time intervals average rate is -40m/30s

confidence rating #$&*:3

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Given Solution:

`aThe slopes and the rates of change are numerically equal. For example between the second and third points the rise of -20 represents the -20 cm change in depth and the run of 50 represents the 50 seconds required to make this change, so the slope represents the -20 cm / (50 sec) average rate of change over the second time interval. We therefore see that slope represents average rate of change.

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Question: `q003. To what extent do you think your graph with three points and straight line segments between them accurately depicts the detailed behavior of the water over the 80-second period of observation?

How do you think the actual behavior of the system differs from that of the graph?

How do you think the graph of the actual behavior of the system would differ from that of the graph you made?

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Your solution:

If we drew a straight line it would make us believe that the water flowed out at a CONSTANT rate.

The graph shows that the depth vs time rate is decreasing at a constant rate. We know that not to be true due to the three points drawn are actually the average rates. The line would be curved, the line decreasing with a decreasing rate.

confidence rating #$&*:3

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Given Solution:

`aThe straight line segments would indicate a constant rate of change of depth. It is fairly clear that as depth decreases, the rate of change of depth will decrease, so that the rate of change of depth will not be constant. The graph will therefore never be straight, but will be a curve which is decreasing at a decreasing rate.

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Question: `q004. From the given information, do you think you can accurately infer the detailed behavior of the water depth over the 80-second period? Do you think you can infer the detailed behavior better than you could the values of the stocks? Why or why not?

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Your solution:

The graph tells us that its is actually decreasing and I believe that we can tell what the actual behavior of the graph will look like with the given points. The stocks graph on the other hand no, no one knows what is going to happen on a daily basis.

confidence rating #$&*:3

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Given Solution:

`aIt will turn out that three data points will be sufficient to infer the detailed behavior, provided the data are accurate. However you might or might not be aware of that at this point, so you could draw either conclusion. However it should be clear that the behavior of the water depth is much more predictable than the behavior of the stock market. We don't know on a given day whether the market will go up or down, but we do know that if we shoot a hole in the bottom of a full bucket the water level will decrease, and we expect that identical holes in identical buckets should result in the same depth vs. clock time behavior.

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&#Good work. Let me know if you have questions. &#