Step 1: Set up the proportional relationship.
By Little's law, inventory \( I = R \times T \), where \( R \) is the production rate and \( T \) is the processing time. Since the production rate \( R \) is not changing in this problem, inventory is directly proportional to the processing time alone, so any percentage change in \( T \) shows up as the same percentage change in \( I \).
Step 2: Apply the 30% cut in processing time.
The processing time is brought down by 30%, so \( T_2 = 0.7\,T_1 \). Because \( I \) is proportional to \( T \) at constant \( R \), \( I_2 = 0.7\,I_1 \), which means the inventory also falls by exactly 30%.
\[ \boxed{\text{Inventory decreases by } 30\%} \]