VBA language macro

HansVogelaar 

Some improvements for your consideration (untested)....

Sub CargoSed()
    Dim VarSed As Range
    Dim x As Double                      ' NEVER use type Single!
    For Each VarSed In Worksheets("Cargo por tratamiento").Range("U4:U24")
        If VarSed < 0.1 Then
            VarSed = 0
        Else
            Select Case VarSed.Value2    ' Value2 is more reliable
                Case Is < 0.5: x = 1.71
                Case Is < 1: x = 2.1
                Case Is < 1.5: x = 2.34
                Case Is < 2: x = 52
                Case Is < 2.5: x = 2.68
                Case Is < 3: x = 2.81
                Case Is < 3.5: x = 2.92
                Case Is < 4: x = 3.03
                Case Is < 4.5: x = 3.11
                Case Is < 5: x = 3.2
                Case Is < 5.5: x = 3.29
                Case Is < 6: x = 3.39
                Case Is < 6.5: x = 3.49
                Case Is < 7: x = 3.6
                Case Is < 7.5: x = 3.7
                Case Is < 8: x = 3.82
                Case Is < 8.5: x 3.93
                Case Is < 9: x = 4.05
                Case Is < 9.5: x = 4.16
                Case Is < 10: x = 4.292
                Case Else: x = 4.42
            End Select
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*" & x
        End If
    Next VarSed
End Sub

Edit....  In hindsight, I see that Octavio_RamosMy_usern  wrote "I am starting to work [...] with the If...Then...Else statement".  So maybe he would prefer that construct for educational purposes.  But I would still just calculate a variable x in the If...Then...Else construct and append it to the rest of the formula in one statement.

Octavio_RamosMy_usern:  Note some subtleties:

1. Always use type Double, not Single.  It  makes no difference in this context.  But it can make a significant difference if you store the variable directly into an Excel cell.  For example:

Dim x As Single

x = 4.292

[a1].Value2 = x

results in 4.29199981689453 in A1, not 4.292.

And the same anomaly can happen in VBA assignments if you mix type Single and Double variables.

2. In general, Value2 is more reliable than Value (which is the default, if omitted).  Again, I suspect that it makes no difference in this context.  But it can have a significant affect on the VBA interpretation of cell values that are formatted as some form of Currency or Accounting and Date.

This comment is mostly just to raise your awarenesss of the issue.  I am not as "religious" about using Value2 as I am about using type Double.  Truth be told, I often omit even the Value property, as HansV did.  Then I spend hours debugging when something mysterious happens, only to discover that I should have used Value or Value2.  Better to be safe than sorry when you are just "starting to work with VBA".

Octavio_RamosMy_usern 

I have received your email. Here is a new version of your macro (also sent in reply to your email):

Sub CargoSed()
    Dim VarSed As Range
    For Each VarSed In Worksheets("Cargo por tratamiento").Range("U4:U24")
        If VarSed < 0.1 Then
            VarSed = 0
        ElseIf VarSed < 0.5 Then
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*1.71"
        ElseIf VarSed < 1 Then
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*2.10"
        ElseIf VarSed < 1.5 Then
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*2.34"
        ElseIf VarSed < 2 Then
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*2.52"
        ElseIf VarSed < 2.5 Then
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*2.68"
        ElseIf VarSed < 3 Then
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*2.81"
        ElseIf VarSed < 3.5 Then
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*2.92"
        ElseIf VarSed < 4 Then
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*3.03"
        ElseIf VarSed < 4.5 Then
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*3.11"
        ElseIf VarSed < 5 Then
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*3.20"
        ElseIf VarSed < 5.5 Then
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*3.29"
        ElseIf VarSed < 6 Then
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*3.39"
        ElseIf VarSed < 6.5 Then
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*3.49"
        ElseIf VarSed < 7 Then
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*3.60"
        ElseIf VarSed < 7.5 Then
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*3.70"
        ElseIf VarSed < 8 Then
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*3.82"
        ElseIf VarSed < 8.5 Then
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*3.93"
        ElseIf VarSed < 9 Then
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*4.05"
        ElseIf VarSed < 9.5 Then
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*4.16"
        ElseIf VarSed < 10 Then
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*4.292"
        Else
            VarSed.FormulaR1C1 = "=((RC5-R[-1]C5)/1000)*RC2*4.42"
        End If
    Next VarSed
End Sub

Octavio_RamosMy_usern 

Please check whether you have used the correct email address - I haven't received anything (I checked the Spam folder too).

A private message might be easier.