When an ice box is packed with 20 identical bottles of soda, it has a mass of 18.7 kg. When the ice box is packed with 25 identical packets of coffee, it has a mass of 8.85 kg. A bottle of soda weighs 550 g more than a packet of coffee. What is the mass of the empty ice box in kg?
1000 g = 1 kg
550 g = 550 ÷ 1000 = 0.55 kg

Mass of 1 packet of coffee = 1 P
Mass of 1 bottle of soda = 1 P + 0.55

Mass of 25 packets of coffee = 25 P
Mass of 20 bottles of soda = 20(1 P + 0.55) = 20 P + 11 

Ice Box + 20 P = 18.7 - 11 = 7.7
Ice Box + 20 P = 7.7 --- (1)

Ice Box + 25 P = 8.85 --- (2)

(2) - (1)
25 P - 20 P = 8.85 - 7.7 
5 P = 1.15

1 P = 1.15 ÷ 5 = 0.23

20 P = 20 x 0.23 = 4.6

Mass of the empty ice box
= 7.7 - 4.6
= 3.1 kg

Answer(s): 3.1 kg