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.
It's Just Our Turn. There are 15 groups â or broods â of cicadas that are on life cycles of either 13 or 17 years. They appear mostly in the eastern and central parts of the U.S. Last spring, it was a brood in parts of Texas, Oklahoma, Missouri, Kansas, Nebraska and Iowa that had its coming out.