When an ice box is packed with 20 identical bottles of soda, it has a mass of 19.5 kg. When the ice box is packed with 25 identical packets of coffee, it has a mass of 9.15 kg. A bottle of soda weighs 590 g more than a packet of coffee. 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 coffee = 1 P
Mass of 1 bottle of soda = 1 P + 0.59

Mass of 25 packets of coffee = 25 P
Mass of 20 bottles of soda = 20(1 P + 0.59) = 20 P + 11.8 

Ice Box + 20 P = 19.5 - 11.8 = 7.7
Ice Box + 20 P = 7.7 --- (1)

Ice Box + 25 P = 9.15 --- (2)

(2) - (1)
25 P - 20 P = 9.15 - 7.7 
5 P = 1.45

1 P = 1.45 ÷ 5 = 0.29

20 P = 20 x 0.29 = 5.8

Mass of the empty ice box
= 7.7 - 5.8
= 1.9 kg

Answer(s): 1.9 kg