diff --git a/AGENTS.md b/AGENTS.md
index f730256..912936c 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -53,6 +53,8 @@ For a new grade, follow the same pattern:
 3. Include the new grade router from `app/routers/math.py`.
 4. Add tests.
 
+Every time you add a new problem, also add an endpoint curl example on the ENDPOINTS-EXAMPLE.md file.
+
 ## Naming Conventions
 
 - Endpoint paths use the existing style: `/math/grade_1/<problem_name>`.
diff --git a/ENDPOINTS-EXAMPLE.md b/ENDPOINTS-EXAMPLE.md
index 39d8f92..3efe8b0 100644
--- a/ENDPOINTS-EXAMPLE.md
+++ b/ENDPOINTS-EXAMPLE.md
@@ -49,3 +49,20 @@ curl -X POST "http://127.0.0.1:8000/math/grade_1/where_are_more_items" \
     "seed": 1
   }'
 ```
+
+### Compose and decompose numbers
+
+```
+curl -X POST "http://127.0.0.1:8000/math/grade_1/compose_and_decompose_numbers" \
+  -H "Content-Type: application/json" \
+  -d '{
+    "picture": {
+      "id": "cube",
+      "name": "Cube",
+      "image_path": "/images/cube.png"
+    },
+    "whole": 10,
+    "randomize_rows": false,
+    "seed": 1
+  }'
+```
diff --git a/app/problems/grade_1/compose_and_decompose_numbers.py b/app/problems/grade_1/compose_and_decompose_numbers.py
new file mode 100644
index 0000000..b3dc374
--- /dev/null
+++ b/app/problems/grade_1/compose_and_decompose_numbers.py
@@ -0,0 +1,42 @@
+import random
+
+from app.schemas.grade_1.compose_and_decompose_numbers import (
+    ComposeAndDecomposeNumbersProblem,
+    DecompositionRow,
+    PictureAsset,
+)
+
+
+def compose_and_decompose_numbers(
+    picture: dict,
+    whole: int = 10,
+    randomize_rows: bool = False,
+    seed: int | None = None,
+) -> dict:
+    """Generate number decomposition rows for one picture asset."""
+    if whole < 2:
+        raise ValueError("whole must be at least 2")
+
+    selected_picture = PictureAsset.model_validate(picture)
+    pairs = [(first_part, whole - first_part) for first_part in range(whole - 1, 0, -1)]
+
+    if randomize_rows:
+        rng = random.Random(seed)
+        rng.shuffle(pairs)
+
+    problem = ComposeAndDecomposeNumbersProblem(
+        whole=whole,
+        picture=selected_picture,
+        rows=[
+            DecompositionRow(
+                position=index + 1,
+                whole=whole,
+                first_part=first_part,
+                second_part=second_part,
+                picture=selected_picture,
+            )
+            for index, (first_part, second_part) in enumerate(pairs)
+        ],
+    )
+
+    return problem.model_dump()
diff --git a/app/problems/grade_1/images_for_reference/compose-and-decompose-numbers.png b/app/problems/grade_1/images_for_reference/compose-and-decompose-numbers.png
new file mode 100644
index 0000000..dd7fcae
Binary files /dev/null and b/app/problems/grade_1/images_for_reference/compose-and-decompose-numbers.png differ
diff --git a/app/routers/grade_1.py b/app/routers/grade_1.py
index 6cbdf57..c3ec5c3 100644
--- a/app/routers/grade_1.py
+++ b/app/routers/grade_1.py
@@ -1,9 +1,16 @@
 from fastapi import APIRouter, HTTPException
 
+from app.problems.grade_1.compose_and_decompose_numbers import (
+    compose_and_decompose_numbers,
+)
 from app.problems.grade_1.join_pictures_with_quantity import (
     join_pictures_with_quantity,
 )
 from app.problems.grade_1.where_are_more_items import where_are_more_items
+from app.schemas.grade_1.compose_and_decompose_numbers import (
+    ComposeAndDecomposeNumbersProblem,
+    ComposeAndDecomposeNumbersRequest,
+)
 from app.schemas.grade_1.join_pictures_with_quantity import (
     JoinPicturesWithQuantityProblem,
     JoinPicturesWithQuantityRequest,
@@ -16,6 +23,24 @@ from app.schemas.grade_1.where_are_more_items import (
 router = APIRouter(prefix="/grade_1", tags=["Grade 1"])
 
 
+@router.post(
+    "/compose_and_decompose_numbers",
+    response_model=ComposeAndDecomposeNumbersProblem,
+)
+def create_compose_and_decompose_numbers_problem(
+    request: ComposeAndDecomposeNumbersRequest,
+) -> dict:
+    try:
+        return compose_and_decompose_numbers(
+            picture=request.picture.model_dump(),
+            whole=request.whole,
+            randomize_rows=request.randomize_rows,
+            seed=request.seed,
+        )
+    except ValueError as exc:
+        raise HTTPException(status_code=400, detail=str(exc)) from exc
+
+
 @router.post(
     "/join_pictures_with_quantity",
     response_model=JoinPicturesWithQuantityProblem,
diff --git a/app/schemas/grade_1/compose_and_decompose_numbers.py b/app/schemas/grade_1/compose_and_decompose_numbers.py
new file mode 100644
index 0000000..25fca5f
--- /dev/null
+++ b/app/schemas/grade_1/compose_and_decompose_numbers.py
@@ -0,0 +1,30 @@
+from pydantic import BaseModel, Field, PositiveInt
+
+
+class PictureAsset(BaseModel):
+    id: str = Field(min_length=1)
+    name: str = Field(min_length=1)
+    image_path: str = Field(min_length=1)
+
+
+class DecompositionRow(BaseModel):
+    position: PositiveInt
+    whole: PositiveInt
+    first_part: PositiveInt
+    second_part: PositiveInt
+    picture: PictureAsset
+    has_answer_boxes: bool = True
+
+
+class ComposeAndDecomposeNumbersProblem(BaseModel):
+    instructions: str = "Compón y descompón el número."
+    whole: PositiveInt
+    picture: PictureAsset
+    rows: list[DecompositionRow]
+
+
+class ComposeAndDecomposeNumbersRequest(BaseModel):
+    picture: PictureAsset
+    whole: PositiveInt = 10
+    randomize_rows: bool = False
+    seed: int | None = None
diff --git a/tests/test_compose_and_decompose_numbers_endpoint.py b/tests/test_compose_and_decompose_numbers_endpoint.py
new file mode 100644
index 0000000..e207a32
--- /dev/null
+++ b/tests/test_compose_and_decompose_numbers_endpoint.py
@@ -0,0 +1,66 @@
+import unittest
+
+from fastapi.testclient import TestClient
+
+from app.main import create_app
+
+
+class ComposeAndDecomposeNumbersEndpointTest(unittest.TestCase):
+    def setUp(self) -> None:
+        self.client = TestClient(create_app())
+        self.picture = {
+            "id": "cube",
+            "name": "Cube",
+            "image_path": "/images/cube.png",
+        }
+
+    def test_creates_ordered_problem(self) -> None:
+        response = self.client.post(
+            "/math/grade_1/compose_and_decompose_numbers",
+            json={"picture": self.picture},
+        )
+
+        self.assertEqual(response.status_code, 200)
+        problem = response.json()
+        rows = problem["rows"]
+
+        self.assertEqual(problem["instructions"], "Compón y descompón el número.")
+        self.assertEqual(problem["whole"], 10)
+        self.assertEqual(problem["picture"], self.picture)
+        self.assertEqual(len(rows), 9)
+        self.assertEqual(
+            [(row["first_part"], row["second_part"]) for row in rows],
+            [(9, 1), (8, 2), (7, 3), (6, 4), (5, 5), (4, 6), (3, 7), (2, 8), (1, 9)],
+        )
+
+        for row in rows:
+            self.assertEqual(row["whole"], 10)
+            self.assertEqual(row["first_part"] + row["second_part"], 10)
+            self.assertEqual(row["picture"], self.picture)
+
+    def test_can_randomize_rows(self) -> None:
+        response = self.client.post(
+            "/math/grade_1/compose_and_decompose_numbers",
+            json={"picture": self.picture, "randomize_rows": True, "seed": 1},
+        )
+
+        self.assertEqual(response.status_code, 200)
+        rows = response.json()["rows"]
+        ordered_pairs = [(9, 1), (8, 2), (7, 3), (6, 4), (5, 5), (4, 6), (3, 7), (2, 8), (1, 9)]
+        randomized_pairs = [(row["first_part"], row["second_part"]) for row in rows]
+
+        self.assertNotEqual(randomized_pairs, ordered_pairs)
+        self.assertCountEqual(randomized_pairs, ordered_pairs)
+
+    def test_returns_bad_request_for_whole_less_than_two(self) -> None:
+        response = self.client.post(
+            "/math/grade_1/compose_and_decompose_numbers",
+            json={"picture": self.picture, "whole": 1},
+        )
+
+        self.assertEqual(response.status_code, 400)
+        self.assertEqual(response.json(), {"detail": "whole must be at least 2"})
+
+
+if __name__ == "__main__":
+    unittest.main()