Coming from the noun 内（うち） 'within', のうち is a grammar pattern that appears after nouns or numbers, in order to signify 'amongst (A)' in the same way as の中（なか）. Like の中（なか）, のうち is often followed by で. However, it can also be followed by の when attached directly to another number.

• この会社（かいしゃ）のうちでもっとも偉（えら）い人（ひと）は田中（たなか）さんです。
  Among everyone in this company, Tanaka-san is the most important.
• ここにいる５人（にん）のうちで一番（いちばん）給料（きゅうりょう）が高（たか）いのは鈴木（すずき）さんです。
  Among the 5 people that are present here, Suzuki-san has the highest salary.
• 村上（むらかみ）監督（かんとく）が監督（かんとく）した映画（えいが）のうちで、一番（いちばん）好（す）きな映画（えいが）はどれですか。
  Among the movies that Murakami has directed, which is your favorite movie?
• ここにある釣（つり）竿（ざお）、10本（ぽん）のうちの４本（ほん）は海（うみ）釣（づ）り用（よう）だ。
  4 of the 10 fishing rods that are here are for saltwater fishing.

The noun specified by の内（うち） may represent a range or a limit, and is not limited to appearing with numbers. Like の中（なか）, it may also appear followed by から in place of で.

• 学校（がっこう）の科目（かもく）全（すべ）てのうちから、一番（いちばん）好（す）きな科目（かもく）を教（おし）えてください。
  Out of all of your school subjects, what is your favorite subject?
• ここにある100枚（まい）のうちから1枚（まい）引（ひ）いてください。
  Please draw one of the 100 cards here.

のうち is far less common than のなか when specifying 'amongst', due to this, のなか will be the preferred (more natural) option in speech. Additionally, although coming from 内（うち）, the kanji form is far less common than plain hiragana.