npa function for calculating gross receipts when adding customers over a certain duration

gistfile1.rb

# n = number of additional customers per period
# p = amount each customer is charged per period
# a = duration of period to calculate total gross for
# 
# example: customer every 2 weeks, 25 per month, after 6 months: (fn).call(2, 25, 6)
# => 1050
->(n, p, a) { t = 0; a.times { |i| t += (i + 1) * p * n }; t }