Sum column on datatable with 2 different results

i have a datatable with a Column: Total
this is the datatable:

Totale (datatype: decimal)
2,9 
2,9

i need to sum of this comumns, then i tried this code:

 Dim Totale As Double = dt.AsEnumerable().Sum(Function(r) IIf(IsDBNull(r("Totale")), 0, r("Totale")))
Dim Totale As Decimal= dt.AsEnumerable().Where(Function(r) IsDBNull(r("Totale")) = False).Sum(Function(r) r("Totale"))
  Dim Totale As Decimal= Convert.ToDecimal(dt.Compute("SUM(Totale)", "Totale is not null"))

This gives me the result of:

6
6
5,8

wich only the last one is correct! my question is WHY the first 2 sum give me 6 as result
thanks

>Solution :

Because you aren’t casting the r("Totale"), so the iterator sums withouth precission, Try:

Dim Totale As Decimal= dt.AsEnumerable().Sum(Function(r) IIf(IsDBNull(r("Totale")), 0, Convert.ToDecimal(r("Totale"))))