The percentage scores of 40 candidates who took a Health and Safety test are given:

77 44 65 84 52 60 35 83 68 66 50 68 65 57 60 50 93 38 46 55

45 69 61 64 40 66 91 59 61 74 70 75 42 65 85 63 73 84 68 30

a. Construct a frequency table by grouping the data into seven classes with equal-width intervals, where the first class is 30–39. 

b. It is proposed that each of the 40 candidates is awarded one of three grades, A, B or C. Construct a new frequency table that matches with this proposal. 

c. A student plans to display all three versions of the data in separate stem-and-leaf diagrams.

For which version(s) of the data would this not be appropriate? Suggest an alternative type of representation in each case.