I made this cake for a family friend yesterday. He is also a math teacher at our school. I borrowed one of the calculators he uses with his classes and made this replica.
I started by making the fondant: Melt one 16 oz bag of mini marshmallows with 2 Tablespoons water in a large bowl. Melt on 30 second intervals, stirring after each round of 30 seconds...about 1 1/2 minutes total.
Add 3 cups of powdered sugar. Stir until smooth. Put Crisco on the counter. Knead in about 3 more cups of powdered sugar. (There were about 2 cups of powdered sugar left in the 2 lb. bag.) I had a lot of fondant left, so you could probably cut this recipe in half.
Put Crisco around the ball of dough. Cover with Saran wrap. Place in an air-tight container until ready to work with it.
I divided the fondant and made black, gray, yellow, a little green, and a little blue. I also left some white.
I covered the cake with regular frosting. Then I rolled out the fondant and placed it on the cake. I cut the buttons out of the rolled fondant. I wrote the numbers and words on the buttons with a fine writing tip.
The equation on the screen equals his age.