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: 31 kg

Solution:

(A+B+C)/3 = 45
=> A+B+C = 135 ....... (i)
(A+B)/2 = 40
=> A+B = 80 ....... (ii)
(B+C)/2 = 43
=> B+C = 86 ....... (iii)

Putting value of A+B from Eq. (ii) into Eq. (i), we have:

80+C = 135
=> C = 55 ....... (iv)

Now, we put value of C from Eq. (iv) into Eq. (iii),

B+55 = 86
B = 86-55
=> B = 31