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 also species of periodical cicadas, as they're called, that emerge from the ground every 13 years, but we won't see those in 2013 (p eriodical cicadas are different from annual cicadas which come out every year).here are 12 different broods of the 17-year cicada and three different broods of the 13-year cicada. Typically, only one brood emerges in one region at one time, re-entering the above-ground world in extraordinary numbers.