I'm trying to generate grades for my students but keep getting a FALSE in some cells. I can't identify the challenge. The number grades used by my school is as follows:

90-100 = 1

80-89 = 2

70-79 = 3

60-69 = 4

55-59 =5

50-54 =6

45-49 =7

40-44 = 8

39 -0 = 9

Please, help. Thank you