<p>this is a PR math problem and i still dont understand even after i read the explanation.</p>
<p>Mrs. Thompson gave a math test that had 30 questions worth 1 point a piece. Mrs thompson doesnt give up any partial credit on questions, and when she scored the test, she found her students got an average of 89% with a STANDARD DEVIATION of 4%. If Katherine scored inside of 3 standard deviations for the test, how many possible percent scores could Katherine have had?</p>
<p>I came out with 7 possible scores (80%, 83.3%, 86.6%, 90%, 93.3%, 96.6%, 100%) and the PR answer is 8 possible scores.( 100%, 97%, 94%, 91%, 88%, 85%, 82%, 79%)</p>
<p>can anyone can explain this to me? Id really appreciate it.</p>
<p>I'd say you were right. On the lower side, Katherine could have a score as low as (89% - (3)(4%)) = 77%, which works out to 23.1 questions right out of 30. There's no partial credit, so Katherine would need to get at least 24 questions right. On the high side, her score could be as high as (89% +(3)(4%)) = 102%, or all 30 questions right. So she can have 24,25,...,29,30 questions right, which works out to the %'s you had calculated.
Looks like someone got careless with the PR answer, and forgot the fact that she could only get an integer #answers right?</p>
<p>Agreed. You were right. Nothing like PR and Kaplan to make you rack your brain over a bad question. I once found 14 errors in one test in a Kaplan book (not an SAT, though.)</p>
<p>thank you optimizerdad, peteSAT
this stupid question cost me several hours#$%^&*</p>