C’s share of profit = 1/5, to be taken by A and B equally.
A gains = 1/5 X 1/2 = 1/10
B gains = 1/5 X 1/2 = 1/10
New share of A = 2/5 + 1/10 = 4/10 + 1/10 = 5/10 = 1/2
New share of B = 2/5 + 1/10 = 4/10 + 1/10 = 5/10 = 1/2
New profit sharing ratio of A and B = 1:1