The total weight of a rubber ball and a mini-helicopter is 2.8 kg. The total weight of a rubber ball and a toy car is 4.9 kg. If the total weight of a toy car and a mini-helicopter is 5.64 kg, find the total weight of the rubber ball, the mini-helicopter and the toy car.
Let 1 rubber ball be 1 R.
Let 1 mini-helicopter be 1 M.
Let 1 toy car be 1 C.

1 R + 1 M = 2.8 --- (1)
1 R + 1 C = 4.9 --- (2)
1 C + 1 M = 5.64 --- (3)

(1) + (2) + (3)
1 R + 1 M + 1 R + 1 C + 1 C + 1 M = 2.8 + 4.9 + 5.64
2 R + 2 M + 2 C = 13.34
2(1 R + 1 M + 1 C) = 13.34 

1 R + 1 M + 1 C = 13.34 ÷ 2
1 R + 1 M + 1 C = 6.67

 Total weight of the rubber ball, the mini-helicopter and the toy car = 6.67 kg

Answer(s): 6.67 kg