Answer:
Sample mean
Symbol: 
Step-by-step explanation:
Given



Solving (a): Is it sample mean or population mean
From the question, we understand that 10 were selected from a total of 30.
And the mean of the selected 10 is 5'2"
The selected 10 is referred to as sample and the mean of the 10 is the sample mean
Solving (b): Symbol to use.
The symbol for sample mean is: 
Answer:
What is the question. Please provide a question.
Answer:
Step-by-step explanation:
the measure exterior angle of a triangle=sum of measures of two opposite
She can do research- instead of looking for something that is just listed, she should spend time looking for a good deal
She can buy a used phone- a used phone is usually cheaper