The lengths (in cm) of leaves collected from a garden are grouped as follows.
(a) Class Interval : 4 – 8 | 8 – 12 | 12 – 16 | 16 – 20 | 20 – 24
Frequency : 5 | 12 | 18 | 9 | 6
(b) (i) Write the class mark for each class interval.
(c) (ii) Prepare a column showing the product of the frequency of each class and its class mark.
(d) (iii) Hence calculate the arithmetic mean length of the leaves, correct to one decimal place.