Cylinder P and Cylinder Q have a total amount of 2474 mℓ of water. For Cylinder Q and Cylinder R, the total amount of water is 3512 mℓ. The amount of water in Cylinder P is ⁴₇ the amount of water in Cylinder R. What is the average amount of water in the 3 cylinders?
Cylinder P = 4 u
Cylinder R = 7 u 

Cylinder Q + Cylinder P = 2474 --- (1)
Cylinder Q + Cylinder R = 3512 --- (2)

(2) - (1)
(Cylinder Q + Cylinder P) - (Cylinder Q + Cylinder R) = 3512 - 2474
7 u - 4 u = 1038
3 u = 1038

1 u = 1038 ÷ 3 = 346
Cylinder P = 4 u = 346 x 4 = 1384

Cylinder P + Cylinder Q + Cylinder R = 1384 + 3512 = 4896 mℓ

Average amount of water in the 3 cylinders
= 4896 ÷ 3 
= 1632 mℓ

Answer(s): 1632 mℓ