title: have some wondering about matplotlib
body: <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  xx1 = np.random.randint(1,7,100)
  xx2 = np.random.randint(1,7,100)
  dice = xx1 + xx2
  plt.hist(dice,normed = True)
  plt.show()
  </code></pre>
  
  <ol>
  <li>What does normed = True do?</li>
  <li>While doing a ploting, must we open with <code>plt.figure()</code> first?</li>
  <li>To be able to draw a graph by using matplotlib, should it has to be a np array or it can be work with the regular list? eg. <code>range(100)</code>.</li>
  </ol>