When an ice box is packed with 25 identical bottles of coke, it has a mass of 18.55 kg. When the ice box is packed with 35 identical packets of lemonade, it has a mass of 8 kg. A bottle of coke weighs 470 g more than a packet of lemonade. What is the mass of the empty ice box in kg?
1000 g = 1 kg
470 g = 470 ÷ 1000 = 0.47 kg

Mass of 1 packet of lemonade = 1 P
Mass of 1 bottle of coke = 1 P + 0.47

Mass of 35 packets of lemonade = 35 P
Mass of 25 bottles of coke = 25(1 P + 0.47) = 25 P + 11.75 

Ice Box + 25 P = 18.55 - 11.75 = 6.8
Ice Box + 25 P = 6.8 --- (1)

Ice Box + 35 P = 8 --- (2)

(2) - (1)
35 P - 25 P = 8 - 6.8 
10 P = 1.2

1 P = 1.2 ÷ 10 = 0.12

25 P = 25 x 0.12 = 3

Mass of the empty ice box
= 6.8 - 3
= 3.8 kg

Answer(s): 3.8 kg