A student wants to create a multiple regression model to predict the price of a used car with the variables number of prior accidents, original sales price of car, and number of miles on the car. Using logic, are any of the variables irrelevant, and, if so, which one(s)?

A student wants to create a multiple regression model to predict the height of a child with the $x$ variables age, length of foot, and shoe size. Using logic, are any of the variables irrelevant, and, if so, which one(s)?

A student wants to create a multiple regression model to predict the height of a child with the $x$ variables age, length of foot, and shoe size. Using logic, are any of the variables irrelevant, and, if so, which one(s)?