title: Approximute cumulative distribution function (CDF) by the weighted sum of the density function
body: <p> is the pdf of the normal distribution. To approximate the cdf:</p>
  <p>( ≤ ) ≈ [() + ⋯ + ( − 2) + ( − ) + ()],</p>
  <p>e.g.  α = 0.01, a = -100 and k = 0, then the summation is</p>
  <p>( ≤ 0) ≈ 0.01[(−100) + ⋯ + (−0.02) + (−0.01) + (0)]</p>
  <p>The accuracy of the approximation increases with the decrease of the step range α. That means, the smaller the step width is, the more terms we can put between a and k, and the more accurate is the probability.</p>
  <p>Design a python program to compute P(X ≤ k). I am not very clear how the iteration works like what is after ()? What is in the ...</p>