Place value
Every digit in a number has its place value.
Place value is the value represented by a digit in a number on the basis of its position in the number. Each number keeps this order of positions:
1783645:
5 - ones
4 - tens
6 - hundreds
3 - thousands
8 - ten thousands
7 - hundred thousands
1 - millions
The place value of a digit increases by 10 times for every position we move left, e.g.:
2973:
place value of 3 is 3
place value of 7 is 7×10=70
place value of 9 is 9×10×10=900
place value of 2 is 2×10×10×10=2000
Due to this we can write every number in expanded form:
$$2973=3×1+7×10+9×100+2×1000$$
This system of number notation is called decimal system because it uses 10 digits (0, 1, 2 ... 9) to express numbers. Each place value in a number is a power of $10: 10^0 (=1), 10^1 (=10), 10^2 (=100), 10^3 (=1000), 10^4 (=10000)$, etc.
$$2973=$$
$$=3×10^0+7×10^1+9×10^2+2×10^3$$
