2.1.9 Mathics

A grade: { 2, 10, 20, 24, 25, 28, 31, 34, 36, 46, 48 }

B grade: { 19, 37, 40 }

C grade: { 16 }

F grade: { 1, 3, 4, 5, 6, 7, 8, 9, 11, 12, 13, 14, 15, 17, 18, 21, 22, 23, 26, 27, 29, 30, 32, 33, 35, 38, 39, 41, 42, 43, 44, 45, 47, 49, 50 }