When an ice box is packed with 20 identical bottles of soda, it has a mass of 16.3 kg. When the ice box is packed with 35 identical packets of milo, it has a mass of 7.2 kg. A bottle of soda weighs 560 g more than a packet of milo. 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 milo = 1 P
Mass of 1 bottle of soda = 1 P + 0.56

Mass of 35 packets of milo = 35 P
Mass of 20 bottles of soda = 20(1 P + 0.56) = 20 P + 11.2 

Ice Box + 20 P = 16.3 - 11.2 = 5.1
Ice Box + 20 P = 5.1 --- (1)

Ice Box + 35 P = 7.2 --- (2)

(2) - (1)
35 P - 20 P = 7.2 - 5.1 
15 P = 2.1

1 P = 2.1 ÷ 15 = 0.14

20 P = 20 x 0.14 = 2.8

Mass of the empty ice box
= 5.1 - 2.8
= 2.3 kg

Answer(s): 2.3 kg