The following data give the annual salaries (in thousand dollars) of 20 randomly selected health care workers. 50

72

57

38

45

65

37

51

35

62

74

40

68

43

77

61

58

54

65

59

a. Calculate the values of the three quartiles and the interquartile range.
b. Find the approximate value of the 30th percentile.
c. Calculate the percentile rank of 61.