diff --git a/index.js b/index.js
index 4d633a5..a64b0e9 100644
--- a/index.js
+++ b/index.js
@@ -19,7 +19,9 @@ const books = [
  * getTitlesByCategory(books, "소설") // → ["어린왕자", "1984", "해리포터"]
  */
 function getTitlesByCategory(books, category) {
-  // 여기를 작성하세요
+  return books
+    .filter((book) => book.category === category)
+    .map((book) => book.title);
 }
 
 /**
@@ -31,7 +33,9 @@ function getTitlesByCategory(books, category) {
  * getTotalPriceAbove(books, 15000) // → 85000
  */
 function getTotalPriceAbove(books, threshold) {
-  // 여기를 작성하세요
+  return books
+    .filter((book) => book.price >= threshold)
+    .reduce((sum, book) => sum + book.price, 0);
 }
 
 /**
@@ -42,7 +46,7 @@ function getTotalPriceAbove(books, threshold) {
  * isAllSameCategory([{ category: "소설" }, { category: "소설" }], "소설") // → true
  */
 function isAllSameCategory(books, category) {
-  // 여기를 작성하세요
+  return books.every((book) => book.category === category);
 }
 
 // ─────────────────────────────────────────────
@@ -58,7 +62,9 @@ function isAllSameCategory(books, category) {
  * formatBookLabel({ title: "어린왕자", author: "생텍쥐페리" }) // → "어린왕자 - 생텍쥐페리"
  */
 function formatBookLabel(book) {
-  // 여기를 작성하세요
+  const { title, author } = book;
+
+  return `${title} - ${author}`;
 }
 
 /**
@@ -69,7 +75,9 @@ function formatBookLabel(book) {
  * const { first, rest } = splitFirstAndRest(books)
  */
 function splitFirstAndRest(books) {
-  // 여기를 작성하세요
+  const [first, ...rest] = books;
+
+  return { first, rest };
 }
 
 /**
@@ -81,7 +89,9 @@ function splitFirstAndRest(books) {
  * omitPrice({ title: "어린왕자", price: 12000 }) // → { title: "어린왕자" }
  */
 function omitPrice(book) {
-  // 여기를 작성하세요
+  const { price, ...rest } = book;
+
+  return rest;
 }
 
 // ─────────────────────────────────────────────
@@ -96,7 +106,17 @@ function omitPrice(book) {
  * // → Map { "소설" => ["어린왕자", "1984", "해리포터"], "교육" => [...] }
  */
 function groupByCategory(books) {
-  // 여기를 작성하세요
+  return books.reduce((map, book) => {
+    const { category, title } = book;
+
+    if (!map.has(category)) {
+      map.set(category, []);
+    }
+
+    map.get(category).push(title);
+
+    return map;
+  }, new Map());
 }
 
 /**
@@ -108,7 +128,9 @@ function groupByCategory(books) {
  * intersection([1, 2, 3], [2, 3, 4]) // → [2, 3]
  */
 function intersection(arrA, arrB) {
-  // 여기를 작성하세요
+  const setB = new Set(arrB);
+
+  return [...new Set(arrA.filter((item) => setB.has(item)))];
 }
 
 /**
@@ -119,7 +141,7 @@ function intersection(arrA, arrB) {
  * unique([1, 2, 2, 3]) // → [1, 2, 3]
  */
 function unique(arr) {
-  // 여기를 작성하세요
+  return [...new Set(arr)];
 }
 
 // ─────────────────────────────────────────────
@@ -134,7 +156,9 @@ function unique(arr) {
  * getOutOfStock({ 어린왕자: 3, "1984": 0 }) // → ["1984"]
  */
 function getOutOfStock(stock) {
-  // 여기를 작성하세요
+  return Object.entries(stock)
+    .filter(([_, quantity]) => quantity === 0)
+    .map(([title]) => title);
 }
 
 /**
@@ -145,7 +169,10 @@ function getOutOfStock(stock) {
  * getTotalStock({ 어린왕자: 3, "1984": 0, 해리포터: 2 }) // → 5
  */
 function getTotalStock(stock) {
-  // 여기를 작성하세요
+  return Object.values(stock).reduce(
+    (sum, quantity) => sum + quantity,
+    0
+  );
 }
 
 /**
@@ -156,7 +183,11 @@ function getTotalStock(stock) {
  * removeNullish({ title: "어린왕자", author: null }) // → { title: "어린왕자" }
  */
 function removeNullish(obj) {
-  // 여기를 작성하세요
+  return Object.fromEntries(
+    Object.entries(obj).filter(
+      ([_, value]) => value !== null && value !== undefined
+    )
+  );
 }
 
 // ─────────────────────────────────────────────
@@ -174,7 +205,28 @@ function removeNullish(obj) {
  * getAvgPriceByCategory(books) // → { 소설: 15000, 교육: 26000 }
  */
 function getAvgPriceByCategory(books) {
-  // 여기를 작성하세요
+  const grouped = books.reduce((acc, book) => {
+    const { category, price } = book;
+
+    if (!acc[category]) {
+      acc[category] = {
+        sum: 0,
+        count: 0,
+      };
+    }
+
+    acc[category].sum += price;
+    acc[category].count += 1;
+
+    return acc;
+  }, {});
+
+  return Object.fromEntries(
+    Object.entries(grouped).map(([category, info]) => [
+      category,
+      info.sum / info.count,
+    ])
+  );
 }
 
 /**
@@ -187,7 +239,11 @@ function getAvgPriceByCategory(books) {
  * sortBy(books, "title")  // → 제목 가나다순 새 배열
  */
 function sortBy(books, key) {
-  // 여기를 작성하세요
+  return [...books].sort((a, b) => {
+    if (a[key] < b[key]) return -1;
+    if (a[key] > b[key]) return 1;
+    return 0;
+  });
 }
 
 /**
@@ -202,7 +258,12 @@ function sortBy(books, key) {
  * // → [{ title: "어린왕자", price: 12000, category: "소설" }]
  */
 function flattenCategories(categories) {
-  // 여기를 작성하세요
+  return categories.flatMap(({ category, books }) =>
+    books.map((book) => ({
+      ...book,
+      category,
+    }))
+  );
 }
 
 // ─────────────────────────────────────────────
@@ -223,7 +284,11 @@ function flattenCategories(categories) {
  * for (const book of createBookIterator(books)) { ... }
  */
 function createBookIterator(books) {
-  // 여기를 작성하세요
+  function* iterator() {
+    yield* books;
+  }
+
+  return iterator();
 }
 
 /**
@@ -236,7 +301,20 @@ function createBookIterator(books) {
  * paginate(books, 1, 2) // → { data: [books[0], books[1]], totalPages: 3, currentPage: 1 }
  */
 function paginate(books, page, size) {
-  // 여기를 작성하세요
+  const totalPages = Math.ceil(books.length / size);
+
+  if (page < 1 || page > totalPages) {
+    throw new Error("유효하지 않은 페이지 번호입니다.");
+  }
+
+  const start = (page - 1) * size;
+  const end = start + size;
+
+  return {
+    data: books.slice(start, end),
+    totalPages,
+    currentPage: page,
+  };
 }
 
 // ─────────────────────────────────────────────
diff --git a/package-lock.json b/package-lock.json
index e6e7363..4afc3b4 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1278,9 +1278,6 @@
         "arm64"
       ],
       "dev": true,
-      "libc": [
-        "glibc"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -1295,9 +1292,6 @@
         "arm64"
       ],
       "dev": true,
-      "libc": [
-        "musl"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -1312,9 +1306,6 @@
         "loong64"
       ],
       "dev": true,
-      "libc": [
-        "glibc"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -1329,9 +1320,6 @@
         "loong64"
       ],
       "dev": true,
-      "libc": [
-        "musl"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -1346,9 +1334,6 @@
         "ppc64"
       ],
       "dev": true,
-      "libc": [
-        "glibc"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -1363,9 +1348,6 @@
         "riscv64"
       ],
       "dev": true,
-      "libc": [
-        "glibc"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -1380,9 +1362,6 @@
         "riscv64"
       ],
       "dev": true,
-      "libc": [
-        "musl"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -1397,9 +1376,6 @@
         "s390x"
       ],
       "dev": true,
-      "libc": [
-        "glibc"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -1414,9 +1390,6 @@
         "x64"
       ],
       "dev": true,
-      "libc": [
-        "glibc"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -1431,9 +1404,6 @@
         "x64"
       ],
       "dev": true,
-      "libc": [
-        "musl"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [