8 pails and 7 tanks can hold 81.4 litres of water.
1 pail and 1 tank can hold 10.4 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 9 tanks hold?
4. How many litres of water can 4 tanks and 8 pails?

(a)
8 pails + 7 tanks = 81.4 --- (1)
1 pail + 1 tank = 10.4 --- (2)

(2) x 7
1 pail + 1 tank = 10.4
7 pails + 7 tanks = 10.4 x 7
7 pails + 7 tanks = 72.8 --- (3)

(1) - (3)
(8 pails + 7 tanks) - (7 pails + 7 tanks) = 81.4 - 72.8
8 pails + 7 tanks - 7 pails - 7 tanks = 8.6
8 pails - 7 pails + 7 tanks - 7 tanks = 8.6

1 pail = 8.6

Volume of 1 pail = 8.6 ℓ

(b)
Substitute 1 pail = 8.6 into (2).
1 pail + 1 tank = 10.4
8.6 + 1 tank = 10.4

1 tank = 10.4 - 8.6 = 1.8

Volume of 1 tank = 1.8 ℓ

(c)
Volume of 9 tanks
= 9 x 1.8
= 16.2 ℓ

(d)
Volume of 4 tanks and 8 pails
= 4 x 1.8 + 8 x 8.6
= 7.2 + 68.8
= 76 ℓ

Answer(s): (a) 8.6 ℓ; (b) 1.8 ℓ; (c) 16.2 ℓ; (d) 76 ℓ