The heights (in cm) of 40 students of Class 9 are given below:
142, 145, 147, 150, 151, 153, 154, 155, 157, 158,
159, 160, 161, 162, 163, 164, 165, 166, 167, 168,
169, 170, 171, 172, 173, 174, 175, 176, 178, 179,
150, 152, 156, 160, 162, 168, 170, 174, 176, 180
(i) Taking a class width of 4 cm and starting the first class at 140 cm, construct a grouped frequency distribution table for the data.
(ii) Add two additional columns to your table to show cumulative frequency and relative frequency (percentage) for each class.
(iii) Using the completed table, find the percentage of students whose heights are at least 168 cm.