title: How to multiply a single column in a data.frame by a number
body: <p>I would like to know how to muliply a single column by 5 from a txt file that I used a script to read. I only know how to mulitply all of the columns by a number, but not a single column. 
  This is my script for reading the txt file:</p>
  
  <pre><code>d = read.table(file="tst1.txt",header=TRUE)
  </code></pre>