Magic Number 15

Yossi writes the number `15` on the board. Then, Danny adds a digit to the right and a digit to the left of the number written on the board, such that the new number is still divisible by `15`.

Find this number. Is there only one possibility?

Note: The digit added to the left is not zero.

Difficulty level (1 very easy - 10 very hard): 2

Topics:
Number Theory -> Modular Arithmetic / Remainder Arithmetic -> Divisibility Rules -> Divisibility Rules by 3 and 9 Proof and Example -> Constructing an Example / Counterexample Number Theory -> Modular Arithmetic / Remainder Arithmetic -> Divisibility Rules -> Divisibility Rules by 5 and 25 Number Theory -> Division
Sources:
注讚讬 讚诪专讬 Avatar
注讚讬 讚诪专讬 - 5 years ago
115

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