How can I calculate the new quotient if I came to know divisor is increased by one?
Knowing the ratio r = A / B and nothing else about the numbers A and B, there is very little we can say about for example A / (B + 1) or A / (B - 1). We have A = rB. If for example B = 1, then A = r, and A / (B + 1) = r / 2, half the value of A / B. On the other hand, if B = 1,000,000 and A = r*1,000,000 then A / (B + 1) = r * 1,000,000 / 1,000,001 = r - r / 1,000,001, barely different from r. 

In the example A / B = 50 and r = 50, when B is replaced with B + 1, the ratio r changes from 50 to 25 if B = 1, but only from 50 to about 49.999,950 if B = 1,000,000.