8 pails and 7 tanks can hold 87.1 litres of water.
1 pail and 1 tank can hold 11.5 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 7 tanks and 8 pails?

(a)
8 pails + 7 tanks = 87.1 --- (1)
1 pail + 1 tank = 11.5 --- (2)

(2) x 7
1 pail + 1 tank = 11.5
7 pails + 7 tanks = 11.5 x 7
7 pails + 7 tanks = 80.5 --- (3)

(1) - (3)
(8 pails + 7 tanks) - (7 pails + 7 tanks) = 87.1 - 80.5
8 pails + 7 tanks - 7 pails - 7 tanks = 6.6
8 pails - 7 pails + 7 tanks - 7 tanks = 6.6

1 pail = 6.6

Volume of 1 pail = 6.6 ℓ

(b)
Substitute 1 pail = 6.6 into (2).
1 pail + 1 tank = 11.5
6.6 + 1 tank = 11.5

1 tank = 11.5 - 6.6 = 4.9

Volume of 1 tank = 4.9 ℓ

(c)
Volume of 7 tanks
= 7 x 4.9
= 34.3 ℓ

(d)
Volume of 7 tanks and 8 pails
= 7 x 4.9 + 8 x 6.6
= 34.3 + 52.8
= 87.1 ℓ

Answer(s): (a) 6.6 ℓ; (b) 4.9 ℓ; (c) 34.3 ℓ; (d) 87.1 ℓ