When an ice box is packed with 15 identical bottles of coke, it has a mass of 12.35 kg. When the ice box is packed with 30 identical packets of orange juice, it has a mass of 7.7 kg. A bottle of coke weighs 520 g more than a packet of orange juice. What is the mass of the empty ice box in kg?
1000 g = 1 kg
520 g = 520 ÷ 1000 = 0.52 kg

Mass of 1 packet of orange juice = 1 P
Mass of 1 bottle of coke = 1 P + 0.52

Mass of 30 packets of orange juice = 30 P
Mass of 15 bottles of coke = 15(1 P + 0.52) = 15 P + 7.8 

Ice Box + 15 P = 12.35 - 7.8 = 4.55
Ice Box + 15 P = 4.55 --- (1)

Ice Box + 30 P = 7.7 --- (2)

(2) - (1)
30 P - 15 P = 7.7 - 4.55 
15 P = 3.15

1 P = 3.15 ÷ 15 = 0.21

15 P = 15 x 0.21 = 3.15

Mass of the empty ice box
= 4.55 - 3.15
= 1.4 kg

Answer(s): 1.4 kg