5 pails and 4 tanks can hold 50.8 litres of water.
1 pail and 1 tank can hold 11 litres of water.

1. How many litres of water can 1 pail hold?
2. How many litres of water can 1 tank hold?
3. How many litres of water can 3 tanks hold?
4. How many litres of water can 4 tanks and 5 pails?

(a)
5 pails + 4 tanks = 50.8 --- (1)
1 pail + 1 tank = 11 --- (2)

(2) x 4
1 pail + 1 tank = 11
4 pails + 4 tanks = 11 x 4
4 pails + 4 tanks = 44 --- (3)

(1) - (3)
(5 pails + 4 tanks) - (4 pails + 4 tanks) = 50.8 - 44
5 pails + 4 tanks - 4 pails - 4 tanks = 6.8
5 pails - 4 pails + 4 tanks - 4 tanks = 6.8

1 pail = 6.8

Volume of 1 pail = 6.8 ℓ

(b)
Substitute 1 pail = 6.8 into (2).
1 pail + 1 tank = 11
6.8 + 1 tank = 11

1 tank = 11 - 6.8 = 4.2

Volume of 1 tank = 4.2 ℓ

(c)
Volume of 3 tanks
= 3 x 4.2
= 12.6 ℓ

(d)
Volume of 4 tanks and 5 pails
= 4 x 4.2 + 5 x 6.8
= 16.8 + 34
= 50.8 ℓ

Answer(s): (a) 6.8 ℓ; (b) 4.2 ℓ; (c) 12.6 ℓ; (d) 50.8 ℓ