In a least-squares regression model, the residuals are assumed to be random. The following data represent the life expectancy of a female born in the given year.

The least-squares regression equation treating the year as the independent variable is \(\hat{y}=0.1633 x-247.2999\). The residuals from left to right are

(a) Denote residuals above 0 with an \(\mathrm{A}\) and those below 0 with a B to form a sequence.

(b) Test the assumption that the residuals are random at the \(\alpha=0.05\) level of significance.