Question

The average weight of 3 men A, B and C is 84 Kg. Another man D joins the group and the average now becomes 80 kg. If another man E whose weight is 3 kg more than that of D, replaces A then the average weight of B, C, D and E becomes 79 kg. What is the weight of A?

Answer 1

Weight for 3 men (A+B+C) = 84*3 = 252 -------- (i)
Weight of 4 men (A+B+C+D) = 80*4 = 320 ------- (ii)
So, D's weight = (320-252) = 68 kg (by solving eq. (i) & (ii))
then E's weight = (68+3) = 71 kg
Now, B+C+D+E = 79*4=316.....(iii) 
B+C+68+71=316 => B+C = 177.....(iv)
Put value (B+C) in eq. (i) 
A=(252-177) = 75kg