speed control loop percent error
This is an example that appears in the first chapter of the excellent book Feedback Control of Dynamic Systems, from Prof. Gene F. Franklin. The percent error on output is defined as:

$$ \%error = 100 \times\frac{(Y_{cl}\space when\space w=0)-(Y_{cl}\space when\space w\neq0)}{(Y_{cl}\space when\space w=0)}$$

Note that \$(Y_{cl}\space when\space w=0) = \frac{100}{101}\times r\$

Do the math.