>>75
たかだか12要素なんだから、効率なんて無視しておｋ

n=12
month=["Jan","Feb","Mar","Apr","Mey","Jun","Jul","Aug","Sep","Oct","Nov","Dec"]
shipments=[2,6,20,15,8,21,8,22,15,20,1,15]

avg = shipments.inject {|a,b| a + b } / n
upper = shipments.select {|x| avg * 1.5 <= x }.size
middle = shipments.select {|x| avg * 0.5 <= x && x < avg * 1.5 }.size
lower = shipments.select {|x| x < avg * 0.5 }.size
p avg,upper,middle,lower

best_month = month[shipments.index(shipments.max)]
worst_month = month[shipments.index(shipments.min)]
p best_month, worst_month