Rinna answered 80% correctly, so 20% were incorrect.<br><br>
&bull; Percentage incorrect = 100% − 80% = 20%<br>
&bull; Number incorrect = 20% of 45 = \(\frac{20}{100} \times 45\) = \(\frac{1}{5} \times 45\) = 9<br><br>
Final Answer: 9