Cylinder S and Cylinder T have a total amount of 864 mℓ of water. For Cylinder T and Cylinder U, the total amount of water is 4329 mℓ. The amount of water in Cylinder S is ²₅ the amount of water in Cylinder U. What is the average amount of water in the 3 cylinders?
Cylinder S = 2 u
Cylinder U = 5 u 

Cylinder T + Cylinder S = 864 --- (1)
Cylinder T + Cylinder U = 4329 --- (2)

(2) - (1)
(Cylinder T + Cylinder S) - (Cylinder T + Cylinder U) = 4329 - 864
5 u - 2 u = 3465
3 u = 3465

1 u = 3465 ÷ 3 = 1155
Cylinder S = 2 u = 1155 x 2 = 2310

Cylinder S + Cylinder T + Cylinder U = 2310 + 4329 = 6639 mℓ

Average amount of water in the 3 cylinders
= 6639 ÷ 3 
= 2213 mℓ

Answer(s): 2213 mℓ