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
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.
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.
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.