Issue with DAX formula at calculate first year's student retention

[felipetorresv]

Hi all the community,

I'm writing becasue I have the following issue:pic 1Y have the following matrix (pic), showing the number of freshmen student per cohort and their presence trought next years (for example, in cohort 2017, there was 147 and for that set of students, in 2018 there was 123 and today there is 108 (third year) students.

I want to show the same matrix but with the first year's retention, second year retention an so on. I tried with the following DAX formula:

Retención_6_años = VAR 
Year1 = CALCULATE(COUNT(Hoja1[ALU_RUT]);FILTER(ALLSELECTED(Hoja1[AÑO_CURSADO_ING_CARRERA]);Hoja1[AÑO_CURSADO_ING_CARRERA]=1)) 
RETURN DIVIDE(COUNT(Hoja1[ALU_RUT]);Year1) 

where the values of the column "AÑO_CURSADO_ING_CARRERA" of my dataset are the columns of the matrix (pic 1).
BUT, the result are as follows (pic 2):

as yo can see, the first result, 119.23%, should be the result of (155/177), but is clearly not correct. 

Help please!! 

Many thanks in advance...

[v-chuncz-msft]

@felipetorresv 

You may check if DISTINCTCOUNT works.