Answer :

AL2006

Each paper cup is a cone.
The volume if a cone is      (1/3) (pi) (radius)² (height)

Notice, in the picture they labeled the diameter of the cup = 8 cm.
But we need the radius. that's 1/2 of the diameter = 4 cm.

So, the volume of these paper cups is 

                                           (1/3) (pi) (4cm)² (11 cm) = about 184 cm³
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It says that tons of lemons have been sacrificed, and you have
about  37,850  cm³ of lemonade.

How many cups will that fill ?

       37,850 cm³ / 184 cm³ = about 205 cups.
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How many packs of cups do you need to buy ?
Unfortunately, they only come in packs of 50.

1 pack = 50 cups . . . . . not enough
2 packs = 100 cups . . . not enough
3 packs = 150 cups . . . not enough
4 packs = 200 cups . . . oh so close but still not enough

You need to buy 5 packs = 250 cups.
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It started raining, so you only sold 80% of the lemonade that you had.

80% means 0.80
"of" means "times"

You started out with 37,850 cm³ .

You sold  (0.8) x (37,850 cm³) = about  30,280 cm³ of it.

How many cups did you fill with that much lemonade ?
(Remember, each cup holds about 184 cm³.)

         30,280 cm³ / 184 cm³ = about 164 cups sold.

You bought 250 cups to start out.
You sold 164 cups of lemonade.

You had  (250 bought - 164 used) =

               86 clean, unused paper cups, still in the wrappers, left over.