A,B and C enter into a partnership in the ratio 72:43:65 . After 4 months, A increases his share by 50%. If the total profit at the end of one year be Rs. 21600, then B's share in the profit is :

Given ratio of initial investments =  $\frac{7}{2}:\frac{4}{3}:\frac{6}{5}$ = 105 : 40 : 36.

 Let the initial investments be 105x, 40x and 36x.

$\therefore A:B:C = 105x\times 4 + \frac{150}{100}\times 105x\times 8 : 40x\times 12 : 36x\times 12$  

               = 1680x : 480x : 432x = 35 : 10 : 9.

Hence, B's share = $21600\times \frac{10}{54}$ = Rs. 4000.