Use Timer? 

STEP 1) Read the client order. A sample client order might read "I'll have a large pizza, 1/2 pepperoni, 2/5 mushrooms, and 1/10 bacon."

STEP 2) Select the pizza size. In this case, select "large". This will cause the denominator to change to 10, as a large pizza has ten slices.

STEP 3) Select toppings. First select on pepperoni and apply to half of the pizza (5 slices). Next, click on mushrooms and apply to 2/5 of the pizza (4 slices). Finally, click on bacon and apply to 1/10 of the pizza (1 slice). NOTE - if you make a mistake, select a different pizza size and the re-select the original pizza size to get a new pizza.

STEP 4) Click "SEND". If you are correct, you will make a sale. Incorrect pizzas will cost you.

Enjoy the game!