For a given sample size, returns the largest fraction which has been sampled with p x 100
get.f(n, p = 0.05)
the number of grains in the detrital sample
the required level of confidence
the largest fraction that is sampled with at least 100 x p certainty
Vermeesch, Pieter. "How many grains are needed for a provenance study?." Earth and Planetary Science Letters 224.3 (2004): 441-451.