When an ice box is packed with 25 identical bottles of soda, it has a mass of 23.2 kg. When the ice box is packed with 40 identical packets of green tea, it has a mass of 12.1 kg. A bottle of soda weighs 570 g more than a packet of green tea. What is the mass of the empty ice box in kg?
1000 g = 1 kg
570 g = 570 ÷ 1000 = 0.57 kg

Mass of 1 packet of green tea = 1 P
Mass of 1 bottle of soda = 1 P + 0.57

Mass of 40 packets of green tea = 40 P
Mass of 25 bottles of soda = 25(1 P + 0.57) = 25 P + 14.25 

Ice Box + 25 P = 23.2 - 14.25 = 8.95
Ice Box + 25 P = 8.95 --- (1)

Ice Box + 40 P = 12.1 --- (2)

(2) - (1)
40 P - 25 P = 12.1 - 8.95 
15 P = 3.15

1 P = 3.15 ÷ 15 = 0.21

25 P = 25 x 0.21 = 5.25

Mass of the empty ice box
= 8.95 - 5.25
= 3.7 kg

Answer(s): 3.7 kg