When an ice box is packed with 20 identical bottles of soda, it has a mass of 18.8 kg. When the ice box is packed with 30 identical packets of coffee, it has a mass of 9.7 kg. A bottle of soda weighs 560 g more than a packet of coffee. What is the mass of the empty ice box in kg?
1000 g = 1 kg
560 g = 560 ÷ 1000 = 0.56 kg

Mass of 1 packet of coffee = 1 P
Mass of 1 bottle of soda = 1 P + 0.56

Mass of 30 packets of coffee = 30 P
Mass of 20 bottles of soda = 20(1 P + 0.56) = 20 P + 11.2 

Ice Box + 20 P = 18.8 - 11.2 = 7.6
Ice Box + 20 P = 7.6 --- (1)

Ice Box + 30 P = 9.7 --- (2)

(2) - (1)
30 P - 20 P = 9.7 - 7.6 
10 P = 2.1

1 P = 2.1 ÷ 10 = 0.21

20 P = 20 x 0.21 = 4.2

Mass of the empty ice box
= 7.6 - 4.2
= 3.4 kg

Answer(s): 3.4 kg