diff --git a/Chapter17-Moderate/17.3-trailingZeroes.js b/Chapter17-Moderate/17.3-trailingZeroes.js
new file mode 100644
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--- /dev/null
+++ b/Chapter17-Moderate/17.3-trailingZeroes.js
@@ -0,0 +1,16 @@
+/*
+Problem: Write an algorithm which computes the number of trailing zeroes in n factorial.
+*/
+
+function factorial(n) {
+	if (n ===1 ) return 1;
+	return n * factorial(n-1);
+}
+
+function trailingZeroes(n) {
+	var count = Math.floor(n/5);
+	for (var i = 25; n/i >= 1; i *= 5) {
+		count += Math.floor(n/i);
+	}
+	return count;
+}
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diff --git a/Chapter17-Moderate/swapNumbers.js b/Chapter17-Moderate/swapNumbers.js
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index 0000000..e5b9235
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+++ b/Chapter17-Moderate/swapNumbers.js
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+/*
+Write a function to swap a number in place (that is, without any temporary variables).
+*/
+
+function switchVals(a,b) {
+  if (a > b) {
+    a = a - b;
+    b = a + b;
+    a = b - a;
+  }  else if (b > a) {
+    b = b - a;
+    a = a + b;
+    b = a - b;
+  }
+}
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diff --git a/Chapter18-Hard/18.1-addition.js b/Chapter18-Hard/18.1-addition.js
new file mode 100644
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+++ b/Chapter18-Hard/18.1-addition.js
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+/*
+Write a function that adds two numbers. You should not use + or any arithmetic operators.
+*/
+
+//convert numbers to binary in order to perform operations on them
+function add(num1, num2) {
+  let bin1 = num1.toString(2);
+  let bin2 = num2.toString(2);
+  return parseInt(addBinary(bin1, bin2), 2);
+}
+
+//recursively add binary numbers using XOR and AND
+function addBinary(bin1, bin2) {
+  if (bin2 === 0) return bin1;
+  let sum = bin1 ^ bin2;
+  let carry = (bin1 & bin2) << 1;
+  return addBinary(sum, carry);
+}
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