

The area under the part of a normal curve that lies within 1 standard deviation of the mean is approximately 0.68 or 68% within two standard deviations, about 0.95 or 95% and within 3 standard deviations, about 0.997 or 99.7%.This fact may seem unusual, since the curve never touches the x-axis, but once can prove it mathematically by using claculus. The total area under a normal distribution curve is equal to 1.00 or 100%.Theoretically the curve never touches the x-axis but it gets increasingly closer.The curve is continuous that is there are no gaps or holes For each value of x, there is a corresponding value of y.


