First, you want to see how many tubs of ice cream you will need to serve 25 guests. Since you cannot but half of a tub of ice cream you will need to buy more than what you will use. That adds up to three tubs of ice cream. If each one costs $3.99, then 3 times 3.99 = 11.97. So Jojo will spend $11.97 dollars on ice cream.