When an ice box is packed with 25 identical bottles of coke, it has a mass of 19.55 kg. When the ice box is packed with 30 identical packets of orange juice, it has a mass of 8.2 kg. A bottle of coke weighs 490 g more than a packet of orange juice. What is the mass of the empty ice box in kg?
1000 g = 1 kg
490 g = 490 ÷ 1000 = 0.49 kg

Mass of 1 packet of orange juice = 1 P
Mass of 1 bottle of coke = 1 P + 0.49

Mass of 30 packets of orange juice = 30 P
Mass of 25 bottles of coke = 25(1 P + 0.49) = 25 P + 12.25 

Ice Box + 25 P = 19.55 - 12.25 = 7.3
Ice Box + 25 P = 7.3 --- (1)

Ice Box + 30 P = 8.2 --- (2)

(2) - (1)
30 P - 25 P = 8.2 - 7.3 
5 P = 0.9

1 P = 0.9 ÷ 5 = 0.18

25 P = 25 x 0.18 = 4.5

Mass of the empty ice box
= 7.3 - 4.5
= 2.8 kg

Answer(s): 2.8 kg