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Dear Tutor,

I am trying to figure out how to fit a curve to my data using MS excel


The graph is a frequency distribution histogram with time on the x axis split into 5 minute bins and the number of jobs in each bin on the y axis.

I am pretty certain that the data is some kind of log normal distribution.

BIn Frequency

5 0

10 0

15 1

20 4

25 3

30 8

35 11

40 9

45 2

50 7

55 6

60 3

65 3

What I want to do is to find a fitted distribution using the lognormal formula and put in "adjustable" constants.I then want to deduct the sample frequencies from the fitted frequencies to get residuals. I will then take the sum of the squared residuals and place it on the screen at the bottom of the squared residuials column.. Finally, I want to square the residuals (to yield all positive numbers).

Then, I call up Solver. I enter my x values and my adjustable constants (mean, sd and cumulative) press "solve" and I should get a curve that is close to my estimate. Except that I don't.

I am having trouble generating a "fitted" data column since I am not sure how to write out to lognormal funtion in excel - I just can't seem to get it right after three days of trying


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