The total weight of a rubik's cube and a mini-helicopter is 2.8 kg. The total weight of a rubik's cube and a toy train is 5.5 kg. If the total weight of a toy train and a mini-helicopter is 5.97 kg, find the total weight of the rubik's cube, the mini-helicopter and the toy train.
Let 1 rubik's cube be 1 R.
Let 1 mini-helicopter be 1 M.
Let 1 toy train be 1 T.

1 R + 1 M = 2.8 --- (1)
1 R + 1 T = 5.5 --- (2)
1 T + 1 M = 5.97 --- (3)

(1) + (2) + (3)
1 R + 1 M + 1 R + 1 T + 1 T + 1 M = 2.8 + 5.5 + 5.97
2 R + 2 M + 2 T = 14.27
2(1 R + 1 M + 1 T) = 14.27 

1 R + 1 M + 1 T = 14.27 ÷ 2
1 R + 1 M + 1 T = 7.135

 Total weight of the rubik's cube, the mini-helicopter and the toy train = 7.135 kg

Answer(s): 7.135 kg