diff --git a/src/org/interview/intro/Averager.java b/src/org/interview/intro/Averager.java
new file mode 100644
index 0000000..e44adad
--- /dev/null
+++ b/src/org/interview/intro/Averager.java
@@ -0,0 +1,7 @@
+package org.interview.intro;
+
+import java.util.List;
+
+public interface Averager<T> {
+    public T average(List<T> thingsToAverage);
+}
diff --git a/src/org/interview/intro/DoubleAverager.java b/src/org/interview/intro/DoubleAverager.java
new file mode 100644
index 0000000..19b1bd2
--- /dev/null
+++ b/src/org/interview/intro/DoubleAverager.java
@@ -0,0 +1,27 @@
+package org.interview.intro;
+
+import java.util.List;
+
+public class DoubleAverager implements Averager<Double> {
+    public Double average(List<Double> numbers) {
+        verifyNonEmpty(numbers.size());
+
+        Double total = 0.0;
+        for (Double number : numbers) {
+            total += number;
+        }
+
+
+        return total / numbers.size();
+    }
+
+    private void verifyNonEmpty(int count) {
+        if (count <= 1) {
+            throw new EmptyListCannotBeAveraged();
+        }
+    }
+
+    public static class EmptyListCannotBeAveraged extends RuntimeException {
+
+    }
+}
diff --git a/src/org/interview/intro/RunningAverageCalculator.java b/src/org/interview/intro/RunningAverageCalculator.java
new file mode 100644
index 0000000..33c86c0
--- /dev/null
+++ b/src/org/interview/intro/RunningAverageCalculator.java
@@ -0,0 +1,11 @@
+package org.interview.intro;
+
+public class RunningAverageCalculator {
+    public void add(Double number) {
+        throw new UnsupportedOperationException("not implemented yet");
+    }
+
+    public double runningAverage() {
+        throw new UnsupportedOperationException("not implemented yet");
+    }
+}
diff --git a/test/org/interview/intro/DoubleAveragerTest.java b/test/org/interview/intro/DoubleAveragerTest.java
new file mode 100644
index 0000000..b0cf7d0
--- /dev/null
+++ b/test/org/interview/intro/DoubleAveragerTest.java
@@ -0,0 +1,25 @@
+package org.interview.intro;
+
+import org.interview.intro.DoubleAverager.EmptyListCannotBeAveraged;
+import org.junit.Test;
+
+import java.util.Collections;
+
+import static java.util.Arrays.asList;
+import static org.junit.Assert.assertEquals;
+
+public class DoubleAveragerTest {
+    @Test
+    public void shouldAverageABunchOfNumbers() {
+        Averager<Double> averager = new DoubleAverager();
+
+        double average = averager.average(asList(6.0, 6.0, 5.0, 5.0));
+        assertEquals(5.5, average, 0.0);
+    }
+
+    @Test(expected = EmptyListCannotBeAveraged.class)
+    public void emptyListsCannotBeAveraged() {
+        Averager<Double> averager = new DoubleAverager();
+        averager.average(Collections.<Double>emptyList());
+    }
+}
diff --git a/test/org/interview/intro/RunningAverageCalculatorTest.java b/test/org/interview/intro/RunningAverageCalculatorTest.java
new file mode 100644
index 0000000..fc2067d
--- /dev/null
+++ b/test/org/interview/intro/RunningAverageCalculatorTest.java
@@ -0,0 +1,10 @@
+package org.interview.intro;
+
+import org.junit.Test;
+
+public class RunningAverageCalculatorTest {
+    @Test
+    public void yourFirstTestGoesHere() {
+
+    }
+}