The modal class is the class interval with the highest frequency. From the table: Frequency of 1-10: 2 11 - 20: 7 21 - 30: 10 (highest) 31 - 40: 3 41 - 50: 1 Therefore, the modal class is 21-30. The upper-class boundary of a class interval is the upper limit, considering the continuous nature of grouped data (typically 0.5 above the stated upper limit if classes are assumed continuous). For the class 21 - 30, the upper-class boundary is 30.5.