One problem with pay$-$as$-$you$-$go systems is the availability of workers paying into the system. In $1960,q,$ workers contributed for each retired person; however, today only

$$ workers contribute per retired person.

$2\mathrm{.}1$; $2\mathrm{.}8$

$2\mathrm{.}8$; $2\mathrm{.}1$

$5\mathrm{.}1$; $2\mathrm{.}1$

$5\mathrm{.}1$; $2\mathrm{.}8$