title: Calculate quantiles of vector producing unexpected results
body: <p>I was asked to calculate BY HAND the IQR of this data</p>
  <blockquote>
  <p>-1,400    -1,000  -0,600  0,400   1,000   1,700   2,300   2,600   3,300   3,700   4,400   4,600   7,000   7,500   7,700   13,500  18,500</p>
  </blockquote>
  <p>The results are</p>
  <blockquote>
  <p>MEDIAN 3.300<br />
  1  QUARTILE 1<br />
  3  QUARTILE 7<br />
  Q3-Q1=IQR = 7-1=6</p>
  </blockquote>
  <p>My results were also confirmed by R.</p>
  <pre><code>x &lt;- c(-1.400,-1.000,-0.600,0.400,1.000,1.700,2.300,2.600,3.300,3.700,4.400,4.600,7.000,7.500,7.700,13.500,18.500)
  summary(x)
  #   Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
  # -1.400   1.000   3.300   4.424   7.000  18.500 
  </code></pre>
  <p>The problem is that they expect instead this value instead.</p>
  <blockquote>
  <p>1  QUARTILE    0.7<br />
  3 QUARTILE  7.25<br />
  IQR= 6.55</p>
  </blockquote>
  <p>Could someone explain what is happening?
  Where is my miscalculation or misuse?</p>