Forum Discussion
Why Can't I Get These VERY Basic Calculations
Chill! Putting pedantics aside, I assure you that the explanations are very simple. So take a deep breath and read carefully.
My guess is: the "x" values are the all possible outcomes of something, and the "p" values are their probabilities. So the SUM(B2:H2) should indeed be 1 (100%).
The reason why you are getting different results is very simple: the professor is working with exact "p" values, or at least with "p" values that have more than 3 decimal places of precision. The 3dp values that he presents are rounded. And the sum of rounded parts does not always equal the whole.
IMHO, that is the professor's error. He should have done one of several things:
(a) Include a footnote stating something to the effect that "your calculations might differ because the presented numbers have been rounded".
(b) Present sufficient data so that you can calculate the same "p" values that he is working with.
(c) Fudge the presented numbers and dependent calculations so that everything is consistent with the presented numbers.
#c is challenging because Excel represents numbers in binary internally, not decimal, and most decimal fractions cannot be represented exactly in binary.
Instead, they must be approximated. And the binary approximation for the same decimal fraction might vary depending on the magnitude of the number. That is why, for example, 10.01 - 10 = 0.01 returns FALSE(!).
So it is very important that you understand and accept the fact that some Excel calculations might not match mathematical calculations and principles exactly.
-----
The bottom line is: With the understanding of the above, you might expect some differences in calculations.
The question is: What should you do about it: tolerate the differences; or adjust the numbers in order to avoid or at least hide the differences?
I don't know because I don't the purpose of the exercises.
-----
I have much more explanation that should be helpful. But I must take a break right now.
I will post more soon. I just wanted to give you something now to put your mind at ease, and to let you know that the explanation is easy and easy to understand.
More later....
- I agree with JoeUser2004 that a) the problem is most likely the p values being rounded to 3 decimal and b) that this is a professor issue for not giving you the proper information to use. The only thing i have to add is that I agree the L4 and L3 refer to column I and in fact there is 'red ink' showing that I3 = L so apparently there is some confusion happening where m should be = SQRT(I4 - L^2) and then add to the confusion it appears he missed the decimal point. Maybe it is me but it appears that particular value for m appears to be overtyped and not a value from the spreadsheet (i.e. human error).
In the end, from what I see, I think you are correct/on track and the 'solution' is misleading or confusing at best
