diff --git a/README.md b/README.md
index 58beeac..45240a7 100644
--- a/README.md
+++ b/README.md
@@ -68,3 +68,4 @@ This section has moved here: [https://facebook.github.io/create-react-app/docs/d
 ### `npm run build` fails to minify
 
 This section has moved here: [https://facebook.github.io/create-react-app/docs/troubleshooting#npm-run-build-fails-to-minify](https://facebook.github.io/create-react-app/docs/troubleshooting#npm-run-build-fails-to-minify)
+
diff --git a/src/utils/cal.js b/src/utils/cal.js
index cb801eb..8238d03 100644
--- a/src/utils/cal.js
+++ b/src/utils/cal.js
@@ -5,3 +5,18 @@
  * @returns 
  */
 export const add = (a, b) => a + b;
+
+export const sum = (nums) => {
+  if (nums === undefined) return undefined;
+  if (nums.length === 0) return undefined;
+
+  return nums.reduce((acc, row) => acc + row, 0);
+};
+
+export const divide = (a, b) => {
+
+  if (b === 0) {
+    return undefined;
+  }
+  return { quotient: Math.floor(a / b), remainder: a % b };
+};
diff --git a/src/utils/cal.test.js b/src/utils/cal.test.js
index 6584f06..5a7732d 100644
--- a/src/utils/cal.test.js
+++ b/src/utils/cal.test.js
@@ -1,4 +1,4 @@
-import { add } from './cal';
+import { add, sum, divide } from './cal';
 
 test('adds 1 + 2 to equal 3', () => {
   const result = add(1, 2);
@@ -19,3 +19,40 @@ describe('add test', () => {
         }
     );
 });
+
+
+describe('sum test', () => {
+    // add test cases here
+    const cases = [
+        [undefined, undefined],
+        [[], undefined],
+        [[1], 1],
+        [[1, 2], 3],
+    ];
+    test.each(cases)(
+        'test case sum [%p] = %p',
+        (nums, expected) => {
+            const result = sum(nums);
+            expect(result).toBe(expected);
+        }
+    );
+});
+
+describe('divide test', () => {
+    // add test cases here
+    const cases = [
+        [1, 0, undefined],
+        [1, 1, { quotient: 1, remainder: 0 }],
+        [2, 1, { quotient: 2, remainder: 0 }],
+        [3, 1, { quotient: 3, remainder: 0 }],
+        [3, 2, { quotient: 1, remainder: 1 }],
+        [3, 3, { quotient: 1, remainder: 0 }],
+    ];
+    test.each(cases)(
+        'test case divide %p / %p  %p',
+        (a, b, expected) => {
+            const result = divide(a, b);
+            expect(result).toEqual(expected);
+        }
+    );
+});