The total weight of a mini-helicopter and a rubber ball is 2.5 kg. The total weight of a mini-helicopter and a toy car is 5.7 kg. If the total weight of a toy car and a rubber ball is 5.74 kg, find the total weight of the mini-helicopter, the rubber ball and the toy car.
Let 1 mini-helicopter be 1 M.
Let 1 rubber ball be 1 R.
Let 1 toy car be 1 C.

1 M + 1 R = 2.5 --- (1)
1 M + 1 C = 5.7 --- (2)
1 C + 1 R = 5.74 --- (3)

(1) + (2) + (3)
1 M + 1 R + 1 M + 1 C + 1 C + 1 R = 2.5 + 5.7 + 5.74
2 M + 2 R + 2 C = 13.94
2(1 M + 1 R + 1 C) = 13.94 

1 M + 1 R + 1 C = 13.94 ÷ 2
1 M + 1 R + 1 C = 6.97

 Total weight of the mini-helicopter, the rubber ball and the toy car = 6.97 kg

Answer(s): 6.97 kg