Your sentence is grammatically correct, but is also a somewhat political statement. Many people do not like being grouped together and labeled as adjectives, particularly when the adjective is a pejorative one: poor, impoverished, destitute, homeless, etc. It is more politically correct to say "Many of the city's lower-class residents are unable to find housing." Or, "Many of the city's residents who live in poverty are unable to find housing." The use of "residents" here as the noun to be qualified by an adjective or by an epithet or other descriptor gives the people behind the name dignity and humanity. But you will often see sentences like your original one in older texts, and certainly many people today still tend to speak that way. And like I said, the grammar is fine.

Hello, Tulay. That's a good question. Yes, "poor" can be a noun as well as an adjective. Your sentence is a perfect example of "poor" being used as a noun. You would use "poverty" as a noun to describe the state of being poor. I hope this explanation helps.

Yes poor is an adjective and a noun in any dictionary. adjective 1. lacking sufficient money to live at a standard considered comfortable or normal in a society. "they were too poor to afford a telephone" too poor is describing what they could not afford and why. "the city's poor" = used as a noun. "the city's poor people" = used an as adjective.

Yes. English Grammar in Use 4th edition by Raymond Murphy is excellent. The paper copy is reasonably priced and a PDF is floating around the net. Unit 76B. [excerpt] We use the + adjective (without a noun) to talk about groups of people. For example: the young, the old, the elderly, the rich, the poor

Hi Tulay, Yes, you can use "poor" as a collective noun, as in your example sentence. Have a nice day, Shani