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 at least 13 broods of 17-year cicadas and five broods of 13-year cicadas. In Pennsylvania separate populations referred to as broods are present during eight different years in different geographic ranges in the state (Table 1). All of the broods in Pennsylvania require 17 years to reach maturity.