diff --git a/source/sec-Covariance.ptx b/source/sec-Covariance.ptx
index ac65014..2b0983b 100644
--- a/source/sec-Covariance.ptx
+++ b/source/sec-Covariance.ptx
@@ -161,18 +161,24 @@
 
             <row bottom="minor">
               <cell right="minor"><m>Y = 0</m></cell>
-              <cell right="minor">0.12</cell>
-              <cell>0.24</cell>
+              <cell right="minor"><m>0.12</m></cell>
+              <cell><m>0.24</m></cell>
             </row>
 
             <row>
               <cell right="minor"><m>Y = 1</m></cell>
-              <cell right="minor">0.3</cell>
-              <cell>34</cell>
+              <cell right="minor"><m>0.3</m></cell>
+              <cell><m>0.34</m></cell>
             </row>
           </tabular>
         </table>
       </statement>
+
+      <answer>
+        <p>
+          <m>-0.0312</m>.
+        </p>
+      </answer>
     </exercise>
 
     <exercise>
@@ -194,16 +200,16 @@
 
             <row bottom="minor">
               <cell right="minor"><m>Y = 0</m></cell>
-              <cell right="minor">0.08</cell>
-              <cell right="minor">0.16</cell>
-              <cell>0.1</cell>
+              <cell right="minor"><m>0.08</m></cell>
+              <cell right="minor"><m>0.16</m></cell>
+              <cell><m>0.1</m></cell>
             </row>
 
             <row>
               <cell right="minor"><m>Y = 1</m></cell>
-              <cell right="minor">0.14</cell>
-              <cell right="minor">0.2</cell>
-              <cell>0.32</cell>
+              <cell right="minor"><m>0.14</m></cell>
+              <cell right="minor"><m>0.2</m></cell>
+              <cell><m>0.32</m></cell>
             </row>
           </tabular>
         </table>