diff --git a/fixedexercise3.1/NumberToLetterConverter.java b/fixedexercise3.1/NumberToLetterConverter.java
new file mode 100644
index 00000000..e9d13272
--- /dev/null
+++ b/fixedexercise3.1/NumberToLetterConverter.java
@@ -0,0 +1,141 @@
+/**
+ *
+ * @author roberta
+ */
+public abstract class NumberToLetterConverter {
+
+    private static final String[] UNITS = {"", "One ", "Two ", "Three ",
+        "Four ", "Five ", "Six ", "Seven ", "Eight ", "Nine ", "Ten ",
+        "Eleven ", "Twelve ", "Thirteen ", "Fourteen ", "Fifteen ", "Sixteen",
+        "Seventeen", "Eighteen", "Nineteen", "Twenty"};
+    private static final String[] TENS = {"Twenty", "Thirty ", "Forty ",
+        "Fifty ", "Sixty ", "Seventy ", "Eighty ", "Ninety ",
+        "One Hundred "};
+    private static final String[] HUNDREDS = {"One Hundred ", "Two Hundred ",
+        "Three Hundred ", "Four Hundred ", "Five Hundred ", "Six Hundred ",
+        "Seven Hundred ", "Eight Hundred ", "Nine Hundred  "};
+
+    /**
+     * El número es válido si está entre 0 y 999.999.999
+     */
+    public static String convertNumberToLetter(double number)
+            throws NumberFormatException {
+        String converted = new String();
+
+        // validate if a legal number
+        if (number < 0) {
+            throw new IllegalArgumentException("Can't convert negative numbers");
+        }
+        double doubleNumber = Math.rint(number * 100) / 100;
+        if (doubleNumber > 999999999) {
+            throw new NumberFormatException(
+                    "The number is greater than 999.999.999, "
+                    + "isn't possible to convert");
+        }
+
+        String splitNumber[] = String.valueOf(doubleNumber).replace('.', '#').split("#");
+
+        // Descompone el trio de millones 
+        int millon = Integer.parseInt(String.valueOf(getDigitAt(splitNumber[0],
+                8))
+                + String.valueOf(getDigitAt(splitNumber[0], 7))
+                + String.valueOf(getDigitAt(splitNumber[0], 6)));
+        if (millon == 1) {
+            converted = "A million ";
+        }
+        if (millon > 1) {
+            converted = convertNumber(String.valueOf(millon)) + "Millions ";
+        }
+
+        // Descompone el trio de miles - 
+        int miles = Integer.parseInt(String.valueOf(getDigitAt(splitNumber[0],
+                5))
+                + String.valueOf(getDigitAt(splitNumber[0], 4))
+                + String.valueOf(getDigitAt(splitNumber[0], 3)));
+        if (miles == 1) {
+            converted += "One Thousand "; 
+        }
+        if (miles > 1) {
+            converted += convertNumber(String.valueOf(miles)) + "Thousand ";
+        }
+
+        // Descompone el ultimo trio de unidades
+        int cientos = Integer.parseInt(String.valueOf(getDigitAt(
+                splitNumber[0], 2))
+                + String.valueOf(getDigitAt(splitNumber[0], 1))
+                + String.valueOf(getDigitAt(splitNumber[0], 0)));
+        if (cientos == 1) {
+            converted += "One";
+        }
+
+        if (millon + miles + cientos == 0) {
+            converted += "Zero dollars";
+        }
+        if (cientos > 1) {
+            converted += convertNumber(String.valueOf(cientos));
+        }
+
+        // Descompone los centavos
+        int centavos = Integer.parseInt(String.valueOf(getDigitAt(
+                splitNumber[1], 2))
+                + String.valueOf(getDigitAt(splitNumber[1], 1))
+                + String.valueOf(getDigitAt(splitNumber[1], 0)));
+        if (centavos == 1) {
+            converted += " With a cent";
+        }
+        if (centavos > 1) {
+            converted += "and " + centavos
+                    + "/100 Dollars";
+        }
+
+        return converted;
+    }
+
+    /**
+     * Convierte los trios de números que componen las unidades, las decenas y
+     * las centenas del número.
+     */
+    private static String convertNumber(String number) {
+        if (number.length() > 3) {
+            throw new NumberFormatException(
+                    "The maximum length must be 3 digits");
+        }
+
+        String output = new String();
+        if (getDigitAt(number, 2) != 0) {
+            output = HUNDREDS[getDigitAt(number, 2) - 1];
+        }
+
+        int k = Integer.parseInt(String.valueOf(getDigitAt(number, 1))
+                + String.valueOf(getDigitAt(number, 0)));
+
+        if (k <= 20) {
+            output += UNITS[k];
+        } else {
+            if (k > 30 && getDigitAt(number, 0) != 0) {
+                output += TENS[getDigitAt(number, 1) - 2] + "And "
+                        + UNITS[getDigitAt(number, 0)];
+            } else {
+                output += TENS[getDigitAt(number, 1) - 2]
+                        + UNITS[getDigitAt(number, 0)];
+            }
+        }
+
+        // Caso especial con 100
+        if (getDigitAt(number, 2) == 1 && k == 0) {
+            output = "One Hundred";
+        }
+
+        return output;
+    }
+
+    /**
+     * Retorna el dígito numerico en la posición indicada de derecha a izquierda
+     */
+    private static int getDigitAt(String origin, int position) {
+        if (origin.length() > position && position >= 0) {
+            return origin.charAt(origin.length() - position - 1) - 48;
+        }
+        return 0;
+    }
+}
diff --git a/fixedexercise3.1/NumberToLetterConverterTest.java b/fixedexercise3.1/NumberToLetterConverterTest.java
new file mode 100644
index 00000000..3cd15488
--- /dev/null
+++ b/fixedexercise3.1/NumberToLetterConverterTest.java
@@ -0,0 +1,74 @@
+
+import org.junit.After;
+import org.junit.AfterClass;
+import org.junit.Before;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+/**
+ *
+ * @author roberta
+ */
+public class NumberToLetterConverterTest {
+
+    public NumberToLetterConverterTest() {
+    }
+
+    @BeforeClass
+    public static void setUpClass() {
+    }
+
+    @AfterClass
+    public static void tearDownClass() {
+    }
+
+    @Before
+    public void setUp() {
+    }
+
+    @After
+    public void tearDown() {
+    }
+
+    /**
+     * Test of convertNumberToLetter method, of class NumberToLetterConverter.
+     */
+    @Test
+    public void testConvertNumberToLetter() {
+        double number = 0.0;
+        String expResult = "Zero dollars";
+        String result = NumberToLetterConverter.convertNumberToLetter(number);
+        assertEquals(expResult, result);
+
+    }
+
+    /**
+     * Test of convertNumberToLetter method, of class NumberToLetterConverter.
+     */
+    @Test
+    public void test1000ConvertNumberToLetter() {
+        double number = 1000.15;
+        String expResult = "One Thousand and 15/100 Dollars";
+        String result = NumberToLetterConverter.convertNumberToLetter(number);
+        assertEquals(expResult, result);
+
+    }
+
+    /**
+     * Test of convertNumberToLetter method, of class NumberToLetterConverter.
+     */
+    @Test
+    public void testNegative() {
+        double number = -1;
+        //String expResult = "Negative ";
+        try {
+            String result = NumberToLetterConverter.convertNumberToLetter(number);
+            fail("Shouln't convert negative numbers");
+        } catch (IllegalArgumentException e) {
+
+        }
+
+    }
+
+}