A digit is a sign (symbol) for writing numbers. In the decimal numeral system there are only 10 digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.
Digits are like letters in the alphabet. Numbers are composed of them, as words are composed of letters. There are only ten digits, but infinitely many numbers.
A number is a mathematical concept denoting quantity, order, or magnitude. A number can be one-digit (5), two-digit (42), three-digit (123), and so on.
Numbers can be natural, integer, rational, real, complex. In primary school, natural numbers and zero are studied.
Main difference:
The composition of a number is the decomposition of a number into a sum of smaller numbers or into place-value terms. Knowledge of the composition of a number is needed for fast mental arithmetic.
For example, the composition of the number 7: 7 = 1 + 6 = 2 + 5 = 3 + 4 = 4 + 3 = 5 + 2 = 6 + 1.
The composition of the number 10: 10 = 1 + 9 = 2 + 8 = 3 + 7 = 4 + 6 = 5 + 5.
Examples of numbers and digits:
A digit is a sign for writing numbers; there are only 10 of them (0–9). A number is a mathematical value (quantity, order), of which there are infinitely many. A number is written with one or several digits. For example, the number 25 is written with two digits: 2 and 5.
In the decimal numeral system there are only 10 digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.
There are infinitely many numbers. The largest number does not exist: for any number n, you can name n + 1, which is greater than it.
You can compare it with letters and words: the alphabet has a finite number of letters, but there are infinitely many words. Similarly, there are only 10 digits, but infinitely many numbers. Digits are the "letters" of mathematics, from which "words" — numbers — are composed.
