I use these cards in my math center for extra practice with addition facts. Students will take the cards and solve the problem. I sometimes have cubes, whiteboards and scratch paper for them to use, but the goal is mental math. Students will check their answer by poking their pencil, pipe cleaner, coffee stirrer, [I use golf tees.] through the hole by the answer they think is correct. The correct answer is marked on the back with a sticker, happy face, x or checkmark. Once the prep work is done this is an easy center to maintain.
I hope you enjoy this activity and will check out my other self check products [subtraction, missing addends, odd and even] that will be coming soon.