okay, so how do they survive? are there any social security benefits?
If you are really broke, you go to your MP and gov't organisations such as the MCYS, CDAC, etc.
MCYS gives you something like 400 per month, if you are broke. Other organisations like CDAC give out food vouchers etc. Comcare programmes also gives out vouchers and all that stuff, some buy food for you.
MCYS will also rent you a one room HDB in really shitty areas for something like 50-80 bucks rental per month. A lot of broke old people live in such HDBs in Toa Payoh etc.
Medical wise, there is Medifund, which will pay for all your medical bills, so they won't let you die. Or you can also apply for a Medical Card from MCYS which will allow you to get free medical treatments at all public hospital if you are truly broke / have a serious handicap.
But you really need to be broke, they will check your bank accounts, to qualify for all these. It ain't pretty, but you won't die.
There are also programmes where you can receive training and learn a skill in a polytechnic or uni for free. And they help you to find a job later. I think they are called CET or something.