The average weight of A, B and C is 45 kg. If the average weight of A and B be 40 kg andthat of B and C be 43 kg, then the weight of B is:
 average weight of A, B and C is 45 kg
$$\frac{A+B+C}{3}$$ = 45
A+B+C = $$45 \times 3$$ = 135
the average weight of A and B is 40 kg
$$\frac{A+B}{2}$$ = 40
A+B = $$40 \times 2$$ = 80
the average weight of  B and C is 43 kg
$$\frac{B+C}{2}$$ = 43
B+C = $$43 \times 2$$ = 86
adding A+B + B+C = 80 + 86 = 166Â
subtracting A+B+C from this we getÂ
166-135 = 31
B = 31kg
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