add-on: 50% of the cash gain on the sales of the hdb flat + the
balance left in your CPF to pay for the new flat.
since the underlined text is up to 50%, you can choose the
difference of paying up more using CPF or cash according to
different ration of CPF: CASH..
if your CPF got lots of money..you may be able to make it
40%:10% from cpf and cash respectively for your new purchase of hdb
flat.
clarify it with the cpf staff if you need clearer answer.