When an ice box is packed with 25 identical bottles of 100 plus, it has a mass of 16.15 kg. When the ice box is packed with 40 identical packets of milk, it has a mass of 8.6 kg. A bottle of 100 plus weighs 410 g more than a packet of milk. What is the mass of the empty ice box in kg?
1000 g = 1 kg
410 g = 410 ÷ 1000 = 0.41 kg

Mass of 1 packet of milk = 1 P
Mass of 1 bottle of 100 plus = 1 P + 0.41

Mass of 40 packets of milk = 40 P
Mass of 25 bottles of 100 plus = 25(1 P + 0.41) = 25 P + 10.25 

Ice Box + 25 P = 16.15 - 10.25 = 5.9
Ice Box + 25 P = 5.9 --- (1)

Ice Box + 40 P = 8.6 --- (2)

(2) - (1)
40 P - 25 P = 8.6 - 5.9 
15 P = 2.7

1 P = 2.7 ÷ 15 = 0.18

25 P = 25 x 0.18 = 4.5

Mass of the empty ice box
= 5.9 - 4.5
= 1.4 kg

Answer(s): 1.4 kg