Average of month ratio vs previous year

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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 :))