Question related to value of old books?

Have you searched for these books on the second hand book sites, like abebooks, or alibris? I would have done that for you, if you had listed the titles and publisher. From those two sites, you can often get an idea of what other people are asking for similar books, and then you would know what yours are worth. Paperbacks, as a general rule, do not have very high values, simply because they weren't of particularly high quality to begin with. Even if they are in good condition now, they will probably deteriorate in the future.