10 Digits (0 to 9)
In the base-10 system, the 4-digit whole numbers are every number from 1,000 to 9,999. That's 9,000 numbers. If decimals are included, there are a lot more. For example, from .0001 to .9999 alone, there are over 9,000 more.
The place value of each digit is b times the place value of the digit to its right where b is the base for the system: whether that is binary, octal, decimal, duodecimal, hexadecimal, sexagesimal or some other value.
One fewer than the base for the number system.
If you mean a number system analogous (similar) to our decimal system, the base for such a number system can be any integer, 2 or greater. In other words, the base can be 2, 3, 4, 5, etc. You need as many different digits as the size of the base (decimal is in base 10, so you need 10 different digits).
A three digit number cannot be divisible by a 5 digit number - in any base.
14
9,000,000
In the decimal system, 10 times. In another system, where the base is x, it would be x times.
10 Digits (0 to 9)
In the base-10 system, the 4-digit whole numbers are every number from 1,000 to 9,999. That's 9,000 numbers. If decimals are included, there are a lot more. For example, from .0001 to .9999 alone, there are over 9,000 more.
The place value of each digit is b times the place value of the digit to its right where b is the base for the system: whether that is binary, octal, decimal, duodecimal, hexadecimal, sexagesimal or some other value.
One fewer than the base for the number system.
If you mean a number system analogous (similar) to our decimal system, the base for such a number system can be any integer, 2 or greater. In other words, the base can be 2, 3, 4, 5, etc. You need as many different digits as the size of the base (decimal is in base 10, so you need 10 different digits).
In base ten, there are 9000 four digit number, the numbers are from 1000 to 9999. If you allow leading zeros, then there are 10000 numbers. [0000 - 9999]
I don't understand the point or meaning of this question but I have provided a few answers below. I suggest you consider posting future questions in a less ambiguous turn of phrase. 1) For Natural numbers, there are 9 (or 10 if you include zero): 1 to 9 2) If you include negative numbers then there are 18 (or 19 if you include 0) These answers are all in base-10. Thus it is a silly question as a digit is merely a symbol; if you used base-16 (hexadecimal) then there would be 16 single digit numbers etc. A 'digit' is also not a necessary concept for a number system as a digit is only relevant in a number system that is based on a repeating series of characters.
There are 16 symbols. The number of symbols is always the same as the base.