[UbuntuGnome] number counter

Hi all.
Not sure if this is posted in the right area, but I'm new to linux scripting, and working with ubuntu.
I have a school project that requires the user to input an unknown amount of numbers, sum up those numbers, average them and display the biggest and smallest number. so far all I have is this:

sum=0
num=0
echo "enter an many numbers as you like or q to quit."
read num
while [ $num != q ]
do
sum=`expr $num + $sum`
read num
done

And the script has to loop.
any Ideas??
thank you in advance.