Salary of A and B is in the ratio 3 : 4 and expenditure is in the ratio 4 : 5. What is the ratio of their savings?
(I) B's saving is 25% of his salary.
(II) B's salary is Rs. 2500.

Let salary of A be 3x and salary of B be 4x
Let expenditure of A be 4y and B be 5y 
Now Statement 1 says B save 25% of his salary
So savings of B = x
Now we can say : x= 4x-5y ( As Savings = Income - Expenditure )
we get : 3x =5y
y = 3x/5 Now Therefore savings of A : 3x-4y = 3x- 4(3x/5)
And then we can calculate ratio of savings .
So statement 1 alone is sufficient .
Now Statement 2 says
B's salary is 2500
Now as we do not know anything about expenditure of B so we cannot calculate savings of B and henceforth savings of A
so Statement 2 alone is not sufficient