For a holiday party, Kathleen is making a six-layer torte, which consists of six 10-inch diameter cake layers with a cream topping on each layer. She knows that one recipe of cream will cover 50 square inches of cake. How many batches of the topping?

Each layer has an area of
  area = (π/4)d^2
  area = π/4*10^2 = 25π ≈ 78.5 (square inches)
The total area of 6 layers will be about
  total area = 6*78.5 in^2 = 471 in^2
The number of batches required is
  (number of batches) = (total area)/(area/batch) = 471/50 = 9.42
Kathleen will need to whip up 10 batches of cream topping.