3. The marks obtained in a mathematics test are as shown below.
Scores Frequency 20-24 1 25-29 2 30-34 2 35-39 16 40-44 5 45-49 9 50-54 Calculate: 8 a) the mean (3 marks) b) the median (3 marks) c) the mode (3 marks) d) the standard deviation (3 marks)​