Given the definition: $$ T(n) = aT(n/b) + n^c $$ I am struggling to derive the value of $b$ from the following problem: $$ T (n) = T (4n/5) + O(1) $$
I feel the value is $5/4$, but I am not sure why other than neither $5$ nor $4/5$ looking the right answer.
Whether I am correct or incorrect, please can someone explain the answer; I want to know how I should be thinking about this problem for future reference.
If you let $b=\frac54$, then $$\frac nb=\frac{n}{5/4}=\frac{n}{5/4}\times \frac{4/5}{4/5}=\frac{4n}{5}$$ which matches your original expression.