Are you going by an umbrella school, or are you on your own? If you're on your own you can correct it how you want. I always add up the total answers and then assign points to them to equal 100. So if there are 10 questions they would each (generally) be worth 10 points.
That makes it easy to turn into a percentage which makes it easy to assign a grade.
OTOH, if you're on your own, you don't have to "grade" it at all!
Just mark the ones that are wrong and talk to the student about why they are wrong and have them fix it.