The name “Numbers” is a translation of Arithmoi, from the Septuagint, titled thus because the book contains many statistics, population counts, tribal and priestly figures, and other numerical data.
https://insight.org/resources/bible/the-pentateuch/numbers
The Lord directed the message of Numbers toward the younger generation, children of the former slaves who escaped through the Red Sea. Except for Joshua, Caleb, and Moses, the older generation—everyone twenty years old or older at the time of the first census—died before the completion of Numbers, due to their disobedience and disbelief
https://insight.org/resources/bible/the-pentateuch/numbers
The book was originally titled Tehillim, which means “praise songs” in Hebrew. The English title of “Psalms” originated from the Septuagint’s Greek title Psalmoi, also meaning “songs of praise.”
https://insight.org/resources/bible/the-wisdom-books/psalms
The psalms are organized into five books or collections. They were probably collected gradually, as corporate worship forms developed along with temple worship. It is likely that by the time of Ezra, the books of the Psalter were organized into their final form.
https://insight.org/resources/bible/the-wisdom-books/psalms
The psalms comprised the ancient hymnal of God’s people. The poetry was often set to music—but not always. The psalms express the emotion of the individual poet to God or about God.
https://insight.org/resources/bible/the-wisdom-books/psalms