Fixed some typos. Credit to Darlene Morris.

lang/en_utf8/help/exercise/comparisonofassessments.html

@@ -15,7 +15,7 @@
 <p>The degree of agreement between the student's and teacher's assessment is
     based on the differences between the scores in individual elements
     (actually the squared differences are used). The mean of these differences
-    must to converted into a meaningful grade. The &quot;Comparison of
+    must be converted into a meaningful grade. The &quot;Comparison of
     Assessments&quot; option allows the teacher a degree of control on how
     these comparisons are converted into grades.</p>
 
@@ -23,7 +23,7 @@
     case of an assessment which has ten Yes/No questions. For example the
     assessment might use questions like "Is the chart correctly formatted?",
     "Is the calculated profit $100.66?", etc. Assume there are ten such
-    questions. When the &quot;Very Lax&quot; setting is chosen, prefect
+    questions. When the &quot;Very Lax&quot; setting is chosen, perfect
     agreement between the student's and teacher's assessment gives a grade of
     100%, if there is only one question which does not match the grade is 90%,
     two disagreements give a grade of 80%, three
@@ -44,9 +44,9 @@
     Strict&quot; territory a disagreement in just two questions drops the grade to
     35% and having a single question in disagreement gives a grade of 65%.</p>
 
-<p>This example is sightly artificial as most assessments usually have elements
+<p>This example is slightly artificial as most assessments usually have elements
     which have a range of values rather than just Yes or No. In those cases the
-    comparison is likely to result in somewhat higher grades then the values
+    comparison is likely to result in somewhat higher grades than the values
     indicated above. The various levels (Very Lax, Lax, Fair...) are given so
     that the teacher can fine tune the comparisons. If they feel that the grades
     being given for assessments are too low then this option should be moved