Since there is a noticeable skewness to the right, we will get a poor
approximation of areas if we replace the rectangles by a normal curve.
If the value of *p* were .90 instead of .10,
the binomial histogram would be skewed left. This is typical behavior of
binomial histograms whenever *p* is either too close to 0 or too close to 1.
When is it 'safe' to use the normal curve to approximate binomial probabilities?
A convenient rule of thumb is as follows:

The reader is reminded that normal curve approximations, no matter how close, are still
*approximations*. The binomial formula ( 4.3) should be used to calculate
exact probabilities whenever possible.