FIVE AS A BASE NUMBER
Our fingers and hands are usually the first models we use to deal with numbers. The use of finger patterns to communicate numbers persists well into our adult lives. Whether it is a request for an additional five minutes or a basketball referee signaling to the recording bench, the use of finger patterns provides an ongoing model for numbers.
The reason our number system is based on ten appears obvious. Ten, however, is quite a large base for mental operations. Findings consistently indicate that some students frequently develop mental strategies that use doubles and multiples of five as points of reference. In explaining these findings, van der Berg and van Eerde (1985) note that the spontaneous use of five or ten as reference points reflect numerical relationships implicit in common finger patterns. For example, a student might show eight as five fingers on one hand and three on the other, or as four fingers on each hand.
In short, the legacy of our early finger patterns is a preference for partitioning numbers less than ten into doubles or, making use of the five within the number. A finger pattern for six can emphasise five and one as well as the four more needed to make ten. These negative images, such as how many fingers are down when making six, form the basis of bridging to ten.