Dutch, like other languages, has approximative expressions with two nu
merals, for example: ''twee, drie boeken'' (lit. two, three books; two
or three books). This construction is analysed. It turns out that the
choice of number words is not arbitrary. Various kinds of factor are
involved, as is shown using language materials from large corpora of D
utch texts. The interval between the two numbers has to be 1, 2, 2 1/2
or 5, multiplied by 10(n), at least in the decimal number system. It
is argued that in daily life this set of so-called ''favourite numbers
'' has a special role. Coins and banknotes, prices of special offers,
bidding conventions in auctions are based on, or make use of, this set
of numbers. An explanation for this favouritism is offered in the fra
mework of the triple-code model of human number processing proposed by
Dehaene. The explanation substantiates Dehaene's claim of the existen
ce of an analogue magnitude code used in estimating and comparing. Hum
an cognition seems to be able to perform simple calculations with quan
tities (e.g., halving and doubling), independently of any counting or
number system.