A gray-scale digital camera with 1,000,000 pixels takes a picture (the picture is made of 1,000,000 parts and each part has a certain amount of gray). A histogram is made where the data is the amount of gray in each of these parts. The histogram looks bell-shaped with a mean of 125 gray levels and a standard deviation of 15.
Approximately how many pixels have a gray scale of between 110 and 140?
A. 30
B. 500,000
C. 680,000
D. 950,000