Gibbon Song Duration. A preliminary behavioral study of the Jingdong black gibbon, a primate endemic to the Wuliang Mountains in China, found that the mean song bout duration in the wet season is 12.59 minutes with a standard deviation of 5.31 minutes.

[SOURCE: L. Sheeran et al., “Preliminary Report on the Behavior of the Jingdong Black Gibbon (Hylobates concolor jingdongensis),”

Tropical Biodiversity, Vol. 5(2), pp. 113–125] Assuming that song bout is normally distributed, determine the percentage of song bouts that have durations within

a. one standard deviation to either side of the mean.

b. two standard deviations to either side of the mean.

c. three standard deviations to either side of the mean.