The average weight of A, B and C is 45 kg. If the average weight of A and B be 40 kg and that of B and C be 43 kg, then the weight of B is:

Answer: Option D

Let A, B, C represent their respective weights.
Then, we have :
A + B + C = (45 × 3) = 135.....(i)
A + B = (40 × 2) = 80.....(ii)
B + C = (43 × 2) = 86.....(iii)
Adding (ii) and (iii), we get:
A + 2B + C = 166.....(iv)
Subtracting (i) from (iv), we get: B = 31
∴ B's weight = 31 kg