title: Filtering and then counting distinct values
body: <p>This is for Excel: I've been tasked with counting distinct records after I have filtered the data.  I have 330 rows with column A containing the 'name' and in Column B I have the name of a test that was done for each 'name', which each 'name' could have taken several iterations of the same test.  The test results are in Column C.   </p>
  
  <pre><code>Col A -Student  Col B -Exam          Col C - Grade
  Student 1       Exam 1              .80
  Student 2       Exam 1              .50
  Student 3       Exam 1              .90
  Student 2       Exam 1              .75
  Student 4       Exam 1              .90
  Student 5       Exam 1              .55
  Student 2       Exam 2              .90
  Student 1       Exam 2              .90
  ....            ....                ...
  </code></pre>
  
  <p>If I filter col B for Exam 1, I want to count the unique number of students that have taken Exam 1. </p>