Final answer:
To determine the cost of thirty cupcakes, divide the total cost of five cupcakes by five to find the price per cupcake, and then multiply by thirty. The total cost for thirty cupcakes is $120.
Step-by-step explanation:
If five cupcakes cost $20, the cost per cupcake is $4. Therefore, the cost of one cupcake is $20 divided by 5, which gives us $4. To find the cost of thirty cupcakes, we can multiply the cost per cupcake by the total number of cupcakes desired. So, $4 times 30 equals $120. Hence, thirty cupcakes will cost $120.