Which Regression Line Is Which
The two least-squares regression lines of a dataset (one of $y$ on $x$, the other of $x$ on $y$) are $3x + 2y = 26$ and $6x + y = 31$, but you are not told which is which. What is the correlation coefficient $r$ between $x$ and $y$? Give a reduced fraction.
Related problems & prerequisites
Worth solving first
Source: Classic textbook exercise on the two regression lines; numbers original. Statement written for AxiomIQ.