The cumulative frequency for a given range is the sum of all the relative frequencies that belong to that range.
The CFs for the given grade ranges are
• ≤ 49 :
9/67
• ≤ 59 :
9/67 + 10/67 = 19/67
• ≤ 69 :
9/67 + 10/67 + 10/67 = 29/67
• ≤ 79 :
9/67 + 10/67 + 10/67 + 14/67 = 43/67
• ≤ 89 :
9/67 + 10/67 + 14/67 + 14/67 + 15/67 = 58/67
• ≤ 100 :
9/67 + 10/67 + 10/67 + 14/67 + 15/67 + 9/67 = 67/67 = 1