When an ice box is packed with 20 identical bottles of coke, it has a mass of 16.9 kg. When the ice box is packed with 35 identical packets of orange juice, it has a mass of 7.2 kg. A bottle of coke weighs 590 g more than a packet of orange juice. What is the mass of the empty ice box in kg?
1000 g = 1 kg
590 g = 590 ÷ 1000 = 0.59 kg

Mass of 1 packet of orange juice = 1 P
Mass of 1 bottle of coke = 1 P + 0.59

Mass of 35 packets of orange juice = 35 P
Mass of 20 bottles of coke = 20(1 P + 0.59) = 20 P + 11.8 

Ice Box + 20 P = 16.9 - 11.8 = 5.1
Ice Box + 20 P = 5.1 --- (1)

Ice Box + 35 P = 7.2 --- (2)

(2) - (1)
35 P - 20 P = 7.2 - 5.1 
15 P = 2.1

1 P = 2.1 ÷ 15 = 0.14

20 P = 20 x 0.14 = 2.8

Mass of the empty ice box
= 5.1 - 2.8
= 2.3 kg

Answer(s): 2.3 kg