A container filled with 13 durians has a mass of 14.81 kg. The same container when filled with 6 chikoos has a mass of 1.21 kg. The mass of 1 durian is seven times the mass of 1 chikoo. Find the mass of the container when it is empty. Express the answer in g.
1 kg = 1000 g

14.81 kg = 14810 g
1.21 kg = 1210 g

1 chikoo = 1 u
6 chikoos = 6 x 1 u = 6 u

1 container + 6 chikoos = 1210
1 container + 6 u = 1210 --- (1)

1 durian = 7 u
13 durians = 13 x 7 u = 91 u

1 container + 13 durians = 14810
1 container + 91 u = 14810 --- (2)

(2) - (1)
91 u - 6 u = 14810 - 1210
85 u = 13600

1 u = 13600 ÷ 85 = 160

6 u = 6 x 160 = 960

From (1):
1 container + 6 u = 1210
1 container + 960 = 1210
 
1 container = 1210 - 960 = 250

Mass of 1 container = 250 g

Answer(s): 250 g