When an ice box is packed with 20 identical bottles of soda, it has a mass of 18.2 kg. When the ice box is packed with 30 identical packets of green tea, it has a mass of 10.7 kg. A bottle of soda weighs 510 g more than a packet of green tea. What is the mass of the empty ice box in kg?
1000 g = 1 kg
510 g = 510 ÷ 1000 = 0.51 kg

Mass of 1 packet of green tea = 1 P
Mass of 1 bottle of soda = 1 P + 0.51

Mass of 30 packets of green tea = 30 P
Mass of 20 bottles of soda = 20(1 P + 0.51) = 20 P + 10.2 

Ice Box + 20 P = 18.2 - 10.2 = 8
Ice Box + 20 P = 8 --- (1)

Ice Box + 30 P = 10.7 --- (2)

(2) - (1)
30 P - 20 P = 10.7 - 8 
10 P = 2.7

1 P = 2.7 ÷ 10 = 0.27

20 P = 20 x 0.27 = 5.4

Mass of the empty ice box
= 8 - 5.4
= 2.6 kg

Answer(s): 2.6 kg