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I can't figure out if it's possible to calculate the 3.125 average of monthly ratio without dividing on each month. I mean only using the year totals or year average or some aggregate of year instead of month.

I tried (total of 2018)/ (total of 2017) and avg(2018)/avg(2017) but I don't get the correct result.

Month   2017    2018    2018/2017
1         10      50       5
2         20      60       3
3         30      75      2.5
4         40      80       2
    avg of (5,3,2.5,2)   3.125

sum       100    265      2.65 (265/100)
avg        25    66.25    2.65 (66.25/25)

I am bad at math so please be kind :))

grimdbx
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    Note that dividing 2018 value / 2017 value represents a ratio and NOT "the monthly increase" as you say. A monthly increase comes from difference not division. Be very specific at what you want to know, the the calculation could be determined later. – NoChance Oct 03 '19 at 11:17
  • Thank you, I adjusted the question – grimdbx Oct 03 '19 at 11:21
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    The results are different because $\dfrac {(A+B+C+D)}{(a+b+c+d)} \ne (\dfrac A a + \dfrac B b + \dfrac C c + \dfrac D d)$ – Mauro ALLEGRANZA Oct 03 '19 at 11:49
  • As said, the 2 calculations are different. In general, regardless of the specific values (unless all are equal), The average of the sums is not arithmetically equal to the sum of averages. – NoChance Oct 03 '19 at 11:54
  • @Mauro ALLEGRANZA 40 and 106 it was supposed to be average of year but it was wrong, sorry I adjusted the question. – grimdbx Oct 03 '19 at 11:55
  • Ok I can see they are different, what I am asking is there any formula that doesn't involve using each month values and only using year totals to reach the 3.125? – grimdbx Oct 03 '19 at 11:57
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    Short answer : NO. – Mauro ALLEGRANZA Oct 03 '19 at 12:02
  • If you insist on your calculation method, use a spreadsheet. – NoChance Oct 03 '19 at 12:06

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