Question

the average weight of A,B,C is 45 kg. if the average weight of A and B is 40 kg and that of B and C is 43 kg , then the weight of B is

Answer 1

Avg. weight of A, B, C = (A+B+C) /3
$\frac{(a + b + c)}{3} = 45 \\ a + b + c = 135$
Avg. weight of A, B = (A+B) /2
$\frac{(a + b)}{2} = 40 \\ a + b = 80$
Avg weight of B, C = (B+C) /2
$\frac{(b + c)}{2} = 43 \\ b + c = 86$
Adding second and third equations
$a + 2b + c = 166$
Subtracting first equation from this equation
$a + 2b + c - a - b - c = 166 - 135 \\ b = 31$
B's weight is 31 kg