Write an explicit formula for a_na n
​
, the n^{\text{th}}n
th
term of the sequence 45, 15, 5, ...45,15,5,

Identify all the cases where non-probability sampling is used when attempting to study the characteristics of a large city. studies on every subject in the population divide a population in groups and obtain a sample studies with a limited amount of time demonstrate existing traits in a population studies with the nth person selected