Question

IB exams

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, what is the weight of B?

Answer 1

the weight 
A + B + C = 45    ⇒ A + B + C = 45 x 3 ⇒ A + B + C = 135........[1]
      3
and A + B = 40    ⇒  A + B = 40 x 2 ⇒  A + B  = 80 ............[2]
          2
and B + C = 43    ⇒  B + C = 43 x 2 ⇒  B + C = 86 ...........[3]
          2 

in [1] put [2]
80 + C = 135 
C = 135 - 80
C = 55

now put C value in [3]
B + 55 = 86
B = 85 - 55
B = 31