What is the difference between number and digit?

The only Difference i think is that Digit is the symbolic representation which is used to represent the numbers. while Number is the expression of quantity

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The difference is like the difference between a Word and a letter. Some Words, such as I or a can be one letter long but most Words are composed of a string of letters. Similarly, 5 or 7 are numbers as well as digits but 57 or 0.57 is a number but not a digit.