diff --git a/Chapter10/optimize-sync/benchmark.js b/Chapter10/optimize-sync/benchmark.js
new file mode 100644
index 0000000..0d180d6
--- /dev/null
+++ b/Chapter10/optimize-sync/benchmark.js
@@ -0,0 +1,23 @@
+const benchmark = require("benchmark");
+const slow = require("./slow");
+const loop = require("./loop");
+const suite = new benchmark.Suite();
+const maxNumber = 100; // number to pass through to sumOfSquares()
+
+suite.add("slow", function () {
+  slow(maxNumber);
+});
+
+suite.add("loop", function () {
+  loop(maxNumber);
+});
+
+suite.on("complete", printResults);
+suite.run();
+
+function printResults() {
+  this.forEach((benchmark) => {
+    console.log(benchmark.toString());
+  });
+  console.log("Fastest implementation is", this.filter("fastest")[0].name);
+}
diff --git a/Chapter10/optimize-sync/loop.js b/Chapter10/optimize-sync/loop.js
new file mode 100644
index 0000000..961cdeb
--- /dev/null
+++ b/Chapter10/optimize-sync/loop.js
@@ -0,0 +1,10 @@
+function sumOfSquares(maxNumber) {
+    let i = 0;
+    let sum = 0;
+    for (i; i <= maxNumber; i++) {
+        sum += i ** 2;
+    }
+    return sum;
+}
+
+module.exports = sumOfSquares;
diff --git a/Chapter10/optimize-sync/package-lock.json b/Chapter10/optimize-sync/package-lock.json
new file mode 100644
index 0000000..e28992a
--- /dev/null
+++ b/Chapter10/optimize-sync/package-lock.json
@@ -0,0 +1,27 @@
+{
+  "name": "optimize-sync",
+  "version": "1.0.0",
+  "lockfileVersion": 1,
+  "requires": true,
+  "dependencies": {
+    "benchmark": {
+      "version": "2.1.4",
+      "resolved": "https://registry.npmjs.org/benchmark/-/benchmark-2.1.4.tgz",
+      "integrity": "sha1-CfPeMckWQl1JjMLuVloOvzwqVik=",
+      "requires": {
+        "lodash": "^4.17.4",
+        "platform": "^1.3.3"
+      }
+    },
+    "lodash": {
+      "version": "4.17.20",
+      "resolved": "https://registry.npmjs.org/lodash/-/lodash-4.17.20.tgz",
+      "integrity": "sha512-PlhdFcillOINfeV7Ni6oF1TAEayyZBoZ8bcshTHqOYJYlrqzRK5hagpagky5o4HfCzzd1TRkXPMFq6cKk9rGmA=="
+    },
+    "platform": {
+      "version": "1.3.6",
+      "resolved": "https://registry.npmjs.org/platform/-/platform-1.3.6.tgz",
+      "integrity": "sha512-fnWVljUchTro6RiCFvCXBbNhJc2NijN7oIQxbwsyL0buWJPG85v81ehlHI9fXrJsMNgTofEoWIQeClKpgxFLrg=="
+    }
+  }
+}
diff --git a/Chapter10/optimize-sync/package.json b/Chapter10/optimize-sync/package.json
new file mode 100644
index 0000000..0110ded
--- /dev/null
+++ b/Chapter10/optimize-sync/package.json
@@ -0,0 +1,15 @@
+{
+  "name": "optimize-sync",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "dependencies": {
+    "benchmark": "^2.1.4"
+  }
+}
diff --git a/Chapter10/optimize-sync/slow.js b/Chapter10/optimize-sync/slow.js
new file mode 100644
index 0000000..4a1a298
--- /dev/null
+++ b/Chapter10/optimize-sync/slow.js
@@ -0,0 +1,13 @@
+function sumOfSquares(maxNumber) {
+  const array = Array.from(Array(maxNumber + 1).keys());
+
+  return array
+    .map((number) => {
+      return number ** 2;
+    })
+    .reduce((accumulator, item) => {
+      return accumulator + item;
+    });
+}
+
+module.exports = sumOfSquares;
\ No newline at end of file