title: Subset tibble of four specific rows
body: <p>I have a tibble, named Alabama, with 31 rows and I want a new tibble made of only rows 1, 11, 21, 31. These rows have are in a column named Year and have the values 1970, 1980, 1990, 2000</p>
  
  <p>I have tried </p>
  
  <pre><code>al_decades &lt;- filter(Alabama, Year==1970 &amp;&amp; Year==1980 &amp;&amp; Year==1990 &amp;&amp; Year==2000)
  </code></pre>
  
  <p>and</p>
  
  <pre><code>al_decades &lt;- subset(Alabama, Year==1970 &amp;&amp; Year==1980 &amp;&amp; Year==1990 &amp;&amp; Year==2000)
  </code></pre>
  
  <p>but neither has worked.</p>