title: How to create breaks using the cut function without numbers overlapping
body: <p>I have a dataset and need to cut the age factor of my dataset into 3 different age categories...e.g. age group 1 (10-20 years old), age group 2 (21-30 years old), and age group 3 (31-40 years old).</p>
  
  <p>If I type
  <code>breaks=c(10, 20, 30, 40)</code> when creating the cut function, the outcome is as follows:
  age group 1 being 10-20
  age group 2 being 20-30
  age group 3 being 30-40</p>
  
  <p>I do not want this! I need age group 2 to be from 21-30 years of age (however 20 is part of this age category now)...I would appreciate some help thank you</p>