The sum of the absolute frequencies is equal to the total number of data, represented bas $$N$$. 1  Relative frequency: the result of dividing the absolute frequency of a certain value by the total number of data.  The sum of the relative frequencies is equal to $$1$$. We can prove this easily by factorizing $$N$$.
Periodical cicadas emerge from underground every 13 or 17 years, depending upon which brood the cicadas belong to. The year a particular brood emerges often differs from other broods and is also dependent on geography. The periodical cicada, although unrelated, is often mistakenly called a locust.
Description and Life Cycle. The adult periodical cicada (Fig. 1) is 1 to 11/2 inches long. The body is black, and legs, eyes and wing veins are reddish-orange. Adults usually emerge in early May in large numbers when the soil temperature 4 inches deep is 67 degrees F.