Да что тут непонятного, любой наркоман знает что decimal system of counting is well established in the English names for numbers. Both the suffix -teen (as in fourteen) and the suffix -ty (as in forty) are related to the word ten. But what about the anomalous eleven and twelve? Why do we not say oneteen, twoteen along the same pattern as thirteen, fourteen, fifteen? Eleven in Old English is endleofan, and related forms in the various Germanic languages point back to an original Germanic *ainlif, "eleven." *Ainlif is composed of *ain-, "one," the same as our one, and the suffix *-lif from the Germanic root *lib-, "to adhere, remain, remain left over." Thus, eleven is literally "one-left" (over, that is, past ten), and twelve is "two-left" (over past ten).