9 pails and 8 tanks can hold 55.7 litres of water.
1 pail and 1 tank can hold 6.6 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 7 tanks hold?
4. How many litres of water can 5 tanks and 9 pails?

(a)
9 pails + 8 tanks = 55.7 --- (1)
1 pail + 1 tank = 6.6 --- (2)

(2) x 8
1 pail + 1 tank = 6.6
8 pails + 8 tanks = 6.6 x 8
8 pails + 8 tanks = 52.8 --- (3)

(1) - (3)
(9 pails + 8 tanks) - (8 pails + 8 tanks) = 55.7 - 52.8
9 pails + 8 tanks - 8 pails - 8 tanks = 2.9
9 pails - 8 pails + 8 tanks - 8 tanks = 2.9

1 pail = 2.9

Volume of 1 pail = 2.9 ℓ

(b)
Substitute 1 pail = 2.9 into (2).
1 pail + 1 tank = 6.6
2.9 + 1 tank = 6.6

1 tank = 6.6 - 2.9 = 3.7

Volume of 1 tank = 3.7 ℓ

(c)
Volume of 7 tanks
= 7 x 3.7
= 25.9 ℓ

(d)
Volume of 5 tanks and 9 pails
= 5 x 3.7 + 9 x 2.9
= 18.5 + 26.1
= 44.6 ℓ

Answer(s): (a) 2.9 ℓ; (b) 3.7 ℓ; (c) 25.9 ℓ; (d) 44.6 ℓ