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.
There are six species of periodical cicadas, three with a 17-year cycle and three with a 13-year cycle. The three species in each life-cycle group are distinctive in size, color, and song. The 17-year cicadas are generally northern, and the 13-year cicadas southern with considerable overlap in their distribution.