When an ice box is packed with 25 identical bottles of soda, it has a mass of 24.1 kg. When the ice box is packed with 30 identical packets of milo, it has a mass of 11.2 kg. A bottle of soda weighs 570 g more than a packet of milo. 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 milo = 1 P
Mass of 1 bottle of soda = 1 P + 0.57

Mass of 30 packets of milo = 30 P
Mass of 25 bottles of soda = 25(1 P + 0.57) = 25 P + 14.25 

Ice Box + 25 P = 24.1 - 14.25 = 9.85
Ice Box + 25 P = 9.85 --- (1)

Ice Box + 30 P = 11.2 --- (2)

(2) - (1)
30 P - 25 P = 11.2 - 9.85 
5 P = 1.35

1 P = 1.35 ÷ 5 = 0.27

25 P = 25 x 0.27 = 6.75

Mass of the empty ice box
= 9.85 - 6.75
= 3.1 kg

Answer(s): 3.1 kg