VB Code:
'loop thru 1(2 since 1 is odd) to 100 skipping every other one (step 2)
Dim sum As Integer
Dim count As Integer
For nmbr As Integer = 2 To 100 Step 2
'increment the count
count += 1
'add to the sum
sum += nmbr
Next
'get average
Dim result As Single = sum / count
'build a string to show results
Dim sb As New System.Text.StringBuilder
sb.Append(String.Format("There a {0} even numbers between 1 and 100.{1}", count, ControlChars.NewLine))
sb.Append(String.Format("The sum of these numbers is {0}.{1}", sum, ControlChars.NewLine))
sb.Append(String.Format("The average of these numbers is {0}.", result))
'show results string
MsgBox(sb.ToString)
If you mean a selection of numbers between 1 and 100 then build off of dynamic_sysop's post.