1. A professor of History is teaching a section of 100 students. Her first exam's grade distribution follows. Calculate the standard deviation for this grouped data.

Exam grades

Frequency

45 to < 50

1

50 to < 55

2

55 to < 60

6

60 to < 65

19

65 to < 70

12

70 to < 75

22

75 to < 80

12

80 to < 85

13

85 to < 90

11

90 to < 95

0

95 to < 100

2