When an ice box is packed with 25 identical bottles of coke, it has a mass of 17.4 kg. When the ice box is packed with 35 identical packets of lemonade, it has a mass of 9.15 kg. A bottle of coke weighs 390 g more than a packet of lemonade. What is the mass of the empty ice box in kg?
1000 g = 1 kg
390 g = 390 ÷ 1000 = 0.39 kg

Mass of 1 packet of lemonade = 1 P
Mass of 1 bottle of coke = 1 P + 0.39

Mass of 35 packets of lemonade = 35 P
Mass of 25 bottles of coke = 25(1 P + 0.39) = 25 P + 9.75 

Ice Box + 25 P = 17.4 - 9.75 = 7.65
Ice Box + 25 P = 7.65 --- (1)

Ice Box + 35 P = 9.15 --- (2)

(2) - (1)
35 P - 25 P = 9.15 - 7.65 
10 P = 1.5

1 P = 1.5 ÷ 10 = 0.15

25 P = 25 x 0.15 = 3.75

Mass of the empty ice box
= 7.65 - 3.75
= 3.9 kg

Answer(s): 3.9 kg