3 pails and 2 tanks can hold 12.7 litres of water.
1 pail and 1 tank can hold 5.2 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 4 tanks hold?
4. How many litres of water can 7 tanks and 3 pails?

(a)
3 pails + 2 tanks = 12.7 --- (1)
1 pail + 1 tank = 5.2 --- (2)

(2) x 2
1 pail + 1 tank = 5.2
2 pails + 2 tanks = 5.2 x 2
2 pails + 2 tanks = 10.4 --- (3)

(1) - (3)
(3 pails + 2 tanks) - (2 pails + 2 tanks) = 12.7 - 10.4
3 pails + 2 tanks - 2 pails - 2 tanks = 2.3
3 pails - 2 pails + 2 tanks - 2 tanks = 2.3

1 pail = 2.3

Volume of 1 pail = 2.3 ℓ

(b)
Substitute 1 pail = 2.3 into (2).
1 pail + 1 tank = 5.2
2.3 + 1 tank = 5.2

1 tank = 5.2 - 2.3 = 2.9

Volume of 1 tank = 2.9 ℓ

(c)
Volume of 4 tanks
= 4 x 2.9
= 11.6 ℓ

(d)
Volume of 7 tanks and 3 pails
= 7 x 2.9 + 3 x 2.3
= 20.3 + 6.9
= 27.2 ℓ

Answer(s): (a) 2.3 ℓ; (b) 2.9 ℓ; (c) 11.6 ℓ; (d) 27.2 ℓ