When an ice box is packed with 25 identical bottles of coke, it has a mass of 21.15 kg. When the ice box is packed with 35 identical packets of orange juice, it has a mass of 8 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 25 bottles of coke = 25(1 P + 0.59) = 25 P + 14.75 

Ice Box + 25 P = 21.15 - 14.75 = 6.4
Ice Box + 25 P = 6.4 --- (1)

Ice Box + 35 P = 8 --- (2)

(2) - (1)
35 P - 25 P = 8 - 6.4 
10 P = 1.6

1 P = 1.6 ÷ 10 = 0.16

25 P = 25 x 0.16 = 4

Mass of the empty ice box
= 6.4 - 4
= 2.4 kg

Answer(s): 2.4 kg