An NGO contracted a construction company to build 2000 houses within one year. In the first half of the year, they built the first 3/5 units of the contracted number. Due to unavoidable circumstances, the company could only build an additional 300 units by October. How many units remain from the contracted number that the company is supposed to build? Let's think first. Chain of thought:
In the first half of the year, the company constructed 3 / 5 * 2000 = 1200 units. The number of units remaining to be built after the company built 1200 units in the first half of the year is 2000 - 1200 = 800. By October, the company built an additional 300 units, thus remaining with 800 - 300 = 500 units to be built.
Therefore, the answer is 500.