I believe in your ratio. As I have already explained earlier,
although I calculated a minimum of 96% employment, most of the
sgreans employed are in government service, the largest employer in
Singapore (SAF alone employs 60.5k regulars [from wiki], and I'm
sure this excludes the admin staff). In addition, you can see a lot
of "self-employed" sgreans in industries like hawkers, taxi
drivers, etc.
Thus, how many sgreans do you think are left to fill up the slots
in these companies? 
In addition, as I have already mentioned in another thread, another
way for a company to "employ" a citizen is to only employ in name,
only paying CPF to the particular citizen, who could be a
housewife. It is a win-win situation: On one hand, the citizen has
more CPF savings for doing nothing. On the other end, the
"employer" pays less corporate tax and has a better citizen to
foreigners ratio, thus enabling him to hire more and cheaper
Foreign workers