The program:

PRINT "Enter + numbers to be averaged. Stop with any negative number"

DO

INPUT prompt "Please enter a positive number ":num

IF num > 0 then

LET sum=sum+num

LET count=count+1

ELSE

LET stop = 10

END IF

LOOP until stop > 0

LET ave = sum/count

PRINT "The average of ";count;" numbers is ";ave

END

Gives output:

Enter + numbers to be averaged. Stop with any negative number

Please enter a positive number 2

Please enter a positive number 15

Please enter a positive number 6

Please enter a positive number 103

Please enter a positive number 13

Please enter a positive number 26

Please enter a positive number 78

Please enter a positive number 4

Please enter a positive number 125

Please enter a positive number -1

The average of 9 numbers is 41.3333