width of curve?

[quazareth]

Hello, I have two sets of data (listed below). Y is logarithmic scale base10 (0.01%-100%). I am required to plot a line on the graph corresponding to 5% of Y & then measure the width of the curve at that line. I am completely lost I've never used charts in excel, any help would be wonderful!

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[MrShorty]

I see two generic approaches to this kind of problem:

1) Regress an equation for y=f(x) (or x=f(y), whichever makes the most sense). Since this looks vaguely like a normal distribution curve (or similar Gaussian curve), that might be a good starting place. Once you have your regressed equation, then you can solve that equation for the two x values that correspond to 5%. The width would be the difference of the two x's

2) Use linear interpolation to find the two x values. This amounts to regressing the straight lines for the two intervals that contain y=5%. Solve those two equations for y=5% to find the two x values.

In many ways, the interpolation approach is often easier, if you have no preference for which approach to use. Are there specific parts of this that you need help with?

[MrShorty]

Response to PM: In your PM, you indicate that you have not learned or done any of the math or Excel needed for this problem. This suggests to me that either you have not taken the required prerequisite courses for the current course, or you are simply having trouble applying the math/Excel you have previously learned to your current course/problem.

Probably the first thing to do is to make certain that your instructor does not expect you to perform the calculation a certain way. If we choose an interpolative approach when the instructor expects you to regress a Gaussian type function, then you likely won't get full marks. If the lack of preliminary instruction in how to do this indicates that your instructor wants you to simply "eyeball" the width visually, then we will waste a lot of effort trying to program a "mathematical" approach when a quick and dirty visual estimate is all the instructor expects.

We will be happy to help you any way we can (without simply doing your homework for you, of course). To avoid doing a lot of unnecessary work, I think we need some idea of how the instructor wants you to do this.

FWIW, if the instructor doesn't care how you do it, I would suggest that a visual "eyeball" estimate will be the easiest.

[quazareth]

Thank you and no I'm not expecting anyone here to-do my homework. There are no prerequisites for this class. I am older than your average "college" student (33) therefore this could be something that's taught in grade 11/12 now that wasn't when I was in highschool. I've gotten a reply from the prof which states:

Hi,

"For 5% line, on the data columns of your excel sheet for the graph, you create an extra column and have all the entries as 5. Now when you draw your main graph you will have line parallel to your x-axis and at the height of 5% on the y-axis."

I can't seem to make this work still and I'm not sure if its because my values on the Y axis aren't actually percentages I just have the cells formatted as such and then the axis is log.... I understand what is requested now I just can't seem to get the chart to make the second line

[MrShorty]

Remember that 5%=0.05. If you enter 5, then it will plot the 2nd line at y=5.00. Try entering 0.05 or 5% instead of just 5