10 REM AVERAGE, TXT
20 DATA 4, 10, 40, 5, 100
30 LET TOTAL = 0
40 FOR N = 1 TO 5
50 READ X
60 LET TOTAL = TOTAL + X
70 NEXT N
80 PRINT "MEAN=: "; TOTAL / 5
90 END

Example 3: A more modern BASIC (for the Newton).