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___________?

Let A, B, C represent their respective weights. Then, we have: A + B + C = (45 x 3) = 135 …. (i) A + B = (40 x 2) = 80 …. (ii) B + C = (43 x 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