When an ice box is packed with 10 identical bottles of 100 plus, it has a mass of 8.1 kg. When the ice box is packed with 20 identical packets of milk, it has a mass of 6.2 kg. A bottle of 100 plus weighs 430 g more than a packet of milk. What is the mass of the empty ice box in kg?
1000 g = 1 kg
430 g = 430 ÷ 1000 = 0.43 kg

Mass of 1 packet of milk = 1 P
Mass of 1 bottle of 100 plus = 1 P + 0.43

Mass of 20 packets of milk = 20 P
Mass of 10 bottles of 100 plus = 10(1 P + 0.43) = 10 P + 4.3 

Ice Box + 10 P = 8.1 - 4.3 = 3.8
Ice Box + 10 P = 3.8 --- (1)

Ice Box + 20 P = 6.2 --- (2)

(2) - (1)
20 P - 10 P = 6.2 - 3.8 
10 P = 2.4

1 P = 2.4 ÷ 10 = 0.24

10 P = 10 x 0.24 = 2.4

Mass of the empty ice box
= 3.8 - 2.4
= 1.4 kg

Answer(s): 1.4 kg