[填空题]
A group of iPhone users particivk:+o io g;z((t rba)vpated in a research survey and the ages of paiw 4s:oy4c9yp)v log 7rticipants were recorded vgo wlyyc7 o 9i4s:4)pin the following table.
It is known that 561. Write down
(1) the modal class;
(2) the mid-interval vaue of the modal class.
2. Determine the class in which the lower quartile lies.
3. Calculate the average age of participants between the ages of 45 and 74 .
The participants in this survey were chosen by randomly selecting people walking past a stand in a shopping mall. However, to be polite, the surveyor only asked people who were by themselves and looked to not be in a hurry.≈
4. Write down the type of sampling method used.
