There is an example problem from p506 of Computer Organization and Design, Fifth Edition: The Hardware/Software interface by David A. Patterson, John L. Hennessy
I wonder how "potential speedup" is defined? The book doesn't give its definition.
In the example, since speedup with $10$ processors is $55\%$ of the potential speedup, the potential speedup should be $ 5.5 / 55\% = 10$. it is equal to the number of processors.
Since the execution time before improvement has a part $(10t)$ unaffectable by parallel computing on multiple processors, according to Amdahl's law (outlined in blue box), the potential speedup must be smaller than the number of processors.
So I am puzzled.
Google books has an earlier (4th) edition which has a similar example too.