1. **State the problem:** We need to find the mode of the number of pages Samir read over 5 days: Monday = 80, Tuesday = 80, Wednesday = 90, Thursday = 80, Friday = 90. 2. **Recall the definition of mode:** The mode is the value that appears most frequently in a data set. 3. **List the data:** $\{80, 80, 90, 80, 90\}$. 4. **Count the frequency of each number:** - 80 appears 3 times. - 90 appears 2 times. 5. **Determine the mode:** Since 80 appears more times than 90, the mode is $80$. **Final answer:** The mode of the numbers is $80$.