What are the importance of decimal numbers?

Answer 1

Human beings have ten fingers so they learned to count in tens. Decimal numbers are based on that. And, following the introduction of the zero into our system of writing numbers, we have decimal numbers in which the value of a digit in the number increases by a multiple of ten for each position moved to the left (and decreases as it moves right).

There is no mathematically intrinsic importance to base ten. After all, most optoelectronic devices use binary (or systems derived from binary, like hexadecimal). If humans had had six fingers (including thumbs) we could have been using a system based on 6.

In fact, in terms of natural measurements (river lengths, mountain heights etc), the most common base is e (2.71828, approx) the base of natural logarithms. But, being a transcendental number, a system based on e would be a nightmare to learn!