For the standard deviation, do I use N or n-1 for the denominator in the formula? And c) and d)

Rockall Raw data is collected from Rockall- the wind speeds, measured in km/h on the fifty days in the study are recorded, in ascending order, in the table below: 23 24 26 29 30 30 34 35 38 39 42 46 47 48 49 49 50 51 51 53 53 55 56 58 59 61 62 64 65 68 68 68 69 70 73 74 74 75 77 81 81 82 85 86 89 90 90 91 94 95 Find the mean, mode and median wind speeds, and comment on your findings. 6) Find the standard deviation of the wind speeds, and explain its relevance. ) Find the upper and lower quartiles of the data, and use them to draw a box and whisker diagram of the wind speeds )Use a scale that goes up to 130 km/h so that you can fit the second data set on it also. 20 Marks a) Mean : 60.14 km/h Mode: 68 km/h Median: 60 km/h