When an ice box is packed with 15 identical bottles of coke, it has a mass of 16.3 kg. When the ice box is packed with 30 identical packets of lemonade, it has a mass of 12.4 kg. A bottle of coke weighs 550 g more than a packet of lemonade. What is the mass of the empty ice box in kg?
1000 g = 1 kg
550 g = 550 ÷ 1000 = 0.55 kg

Mass of 1 packet of lemonade = 1 P
Mass of 1 bottle of coke = 1 P + 0.55

Mass of 30 packets of lemonade = 30 P
Mass of 15 bottles of coke = 15(1 P + 0.55) = 15 P + 8.25 

Ice Box + 15 P = 16.3 - 8.25 = 8.05
Ice Box + 15 P = 8.05 --- (1)

Ice Box + 30 P = 12.4 --- (2)

(2) - (1)
30 P - 15 P = 12.4 - 8.05 
15 P = 4.35

1 P = 4.35 ÷ 15 = 0.29

15 P = 15 x 0.29 = 4.35

Mass of the empty ice box
= 8.05 - 4.35
= 3.7 kg

Answer(s): 3.7 kg