The total weight of a mini-helicopter and a toy rifle is 2.9 kg. The total weight of a mini-helicopter and a toy plane is 4.6 kg. If the total weight of a toy plane and a toy rifle is 5.61 kg, find the total weight of the mini-helicopter, the toy rifle and the toy plane.
Let 1 mini-helicopter be 1 M.
Let 1 toy rifle be 1 T.
Let 1 toy plane be 1 P.

1 M + 1 T = 2.9 --- (1)
1 M + 1 P = 4.6 --- (2)
1 P + 1 T = 5.61 --- (3)

(1) + (2) + (3)
1 M + 1 T + 1 M + 1 P + 1 P + 1 T = 2.9 + 4.6 + 5.61
2 M + 2 T + 2 P = 13.11
2(1 M + 1 T + 1 P) = 13.11 

1 M + 1 T + 1 P = 13.11 ÷ 2
1 M + 1 T + 1 P = 6.555

 Total weight of the mini-helicopter, the toy rifle and the toy plane = 6.555 kg

Answer(s): 6.555 kg