<result_list>
<result>
<id>809678</id>
<grade>9</grade>
</result>
<result>
<id>809630</id>
<grade>8</grade>
</result>
<result>
<id>809679</id>
<grade>10</grade>
</result>
<result>
<id>809673</id>
<grade>6</grade>
</result>
</result_list>
java Average grade grade.xml 8.25