Calculate percentage based on checkbox results in Numbers iOS

Using Numbers iOS, I've created a gradebook to keep track of my students' progress.

I have used the Checkbox format for my results, and I would like to create a formula that will calculate a percentage based off of the checked results.

What formula could I use to convert the TRUE and FALSE results from my checkbox cells into 1s and 0s, add up the score, and then convert the total score into a percentage?

I've attached a picture to help explain what it is I'm trying to do here. I'd like to keep the checkboxes cells as checkboxes and only have the results converted in the "Grade" Column.

Thanks for your help!