Container M and N are identical containers with the same base area and height. Container M is filled to the brim with water while Container N is empty. After 280 cm³ of water from Container M is poured into Container N, the depth of water in Container N is ¹₅ the depth of water in Container M. If the height of Container N is 21 cm, what is the base area of Container N?
The depth of water is proportional to the volume of water.

After water from Container M is poured into Container N:

Volume of water in Container M : Volume of water in Container N
 5 : 1

1 u = 280

Total volume of Container N
= 5 u + 1 u
= 6 u
= 6 x 280
= 1680 cm³

Base area of Container N
= 1680 ÷ 21
= 80 cm²

Answer(s): 80 cm²