The basis of your research should be news article(s) and the latest developments of that particular market/industry and supplemented by other sources such as statistics from official agencies.

Your task is to apply the concept of demand and supply, together with appropriate evidence from the article or other sources, to explain the increase in price.

http://www.straitstimes.com/singapore/housing/hdb-resale-prices-edge-up-in-november-volume-down-srx

http://www.straitstimes.com/singapore/hdb-incurs-202b-deficit-in-last-fy

"But resale volume fell significantly in a month that also saw a record launch of new flats for sale."

The decrease in supply of resale flats may be due to the also with the increase of supply of new flats such as BTO flats. This then increases the price of the resale flats.

As the price of resale flats increase, this would mean that the launch of new flats are cheaper. Hence, supply of resale flats increase.

The decrease in supply of resale flats and the increase in demand of resale flats, results in the increase of the price of resale flats.

For this case, the number of sellers determines the supply of resale flats. Hence, if there are more resale flat owners who wish to sell their flats, the supply of resale flats will then increase.

The law of supply states that there is a direct relationship between price and the quantity supplied of the good. Therefore, the increase in price will result in an increase of quantity supplied. 

This is because when HDB owners find out that price of resale flats increased, they are more likely to sell their HDB flats as it is more profitable.

This will lead to the fallacy of composition. As all flats owners think that it is a good time to sell their flats due the increase in price of resale flats, the price of such flats will drop once supply starts to exceed demand thus making some owners to lose out and be at an disadvantage.

Additionally, as resale flats will be considered as inferior goods when compared to the new flats, the supply of such products will face a decrease in numbers due to the lack of demand for resale flats as people are more willing to buy new flats.

The first determinant to explain for the change in demand of HDB flats and condos would be taste and preferences. Consumers now may prefer condos over HDB flats, thus resulting in the demand for condo to increase, and the demand for HDB flats to decrease. This then causes the Housing Board to incur a loss.

Next, the number of buyers in the market will affect the demand for certain goods. When the number of buyers for condos in the market increases, the demand for condo will increase so as to make sure that buyers are able to get them. Likewise, the number of buyers in the market for HDB flats will decrease causing a drop in total revenue generated from the sales of flats,

However, the deficit incurred caused the rental related business to decrease.

This might also be due to the substitution effect. As the prices of HDB flats increase, more people turn to buying condominiums as they might think its more worth their money and in the eyes of many people it is of a higher social standing.