You have 8 gallons of lemonade to sell. you use cone-shaped cups that are 9 centimeters in diameter and 12 centimeters tall. each customer uses one paper cup. how many paper cups will you need if you sell all of the lemonade? (1 gal ≈ 3785 cm3)

Okay, first figure out how much one cone-shaped cup can hold, this is the volume. Use the formula for the volume of a cone:



Plug in what we know, remember that the radius is half the diameter(9/2 = 4.5), and use 3.14 to approximate for Pi:



Just simplify the exponent and multiply them all:



So this is the amount that one cone-shaped cup holds. You have 8 gallons of lemonade, let's convert this to cubic centimeters:



Now divide the amount that fits in one cup by the total amount to find out how many cups you need to sell to sell all the lemonade:



So you need to sell approximately 119 paper cups to sell all of the lemonade.