Let the weights (in kg) of top 5 students be x1,x2,x3,x4andx5 respectively. Average weight of the top two students =x1+1.5 (∵ average weight increases by one and a half kg each time) ⇒(x+x2)/2=x1+1.5 ⇒x2=x1+3 Similarly, x3=x1+6,x4=x1+9andx5=x1+12 ∴ The last student is heavier than the first student by 12 kg.