When an ice box is packed with 20 identical bottles of coke, it has a mass of 17.1 kg. When the ice box is packed with 30 identical packets of lemonade, it has a mass of 6.6 kg. A bottle of coke weighs 580 g more than a packet of lemonade. What is the mass of the empty ice box in kg?
1000 g = 1 kg
580 g = 580 ÷ 1000 = 0.58 kg

Mass of 1 packet of lemonade = 1 P
Mass of 1 bottle of coke = 1 P + 0.58

Mass of 30 packets of lemonade = 30 P
Mass of 20 bottles of coke = 20(1 P + 0.58) = 20 P + 11.6 

Ice Box + 20 P = 17.1 - 11.6 = 5.5
Ice Box + 20 P = 5.5 --- (1)

Ice Box + 30 P = 6.6 --- (2)

(2) - (1)
30 P - 20 P = 6.6 - 5.5 
10 P = 1.1

1 P = 1.1 ÷ 10 = 0.11

20 P = 20 x 0.11 = 2.2

Mass of the empty ice box
= 5.5 - 2.2
= 3.3 kg

Answer(s): 3.3 kg