A container filled with 10 watermelons has a mass of 10.68 kg. The same container when filled with 5 pears has a mass of 0.93 kg. The mass of 1 watermelon is seven times the mass of 1 pear. Find the mass of the container when it is empty. Express the answer in g.
1 kg = 1000 g

10.68 kg = 10680 g
0.93 kg = 930 g

1 pear = 1 u
5 pears = 5 x 1 u = 5 u

1 container + 5 pears = 930
1 container + 5 u = 930 --- (1)

1 watermelon = 7 u
10 watermelons = 10 x 7 u = 70 u

1 container + 10 watermelons = 10680
1 container + 70 u = 10680 --- (2)

(2) - (1)
70 u - 5 u = 10680 - 930
65 u = 9750

1 u = 9750 ÷ 65 = 150

5 u = 5 x 150 = 750

From (1):
1 container + 5 u = 930
1 container + 750 = 930
 
1 container = 930 - 750 = 180

Mass of 1 container = 180 g

Answer(s): 180 g