[填空题]
A group of iPhone users participated in a research 19rltae3w *5 x7hi;d q/r oqnnsurvey and the ages of partrl7;fugmvt20zh( ca. 8b1 xfcicipants were recovx mff r2.;(80caz u7lgtbh1c rded in 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.
