A multiple of 15 in ones and zeros

What is the least positive multiple of $15$ whose decimal digits are all $1$ s and $0$ s?

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Divisible by $5$ (digits $0/1$ ) $\Rightarrow$ ends in $0$ . Divisible by $3$ $\Rightarrow$ digit sum (number of $1$ s) is a multiple of $3$ .
Fewest $1$ s is $3$ : the number is $1110$ .

Answer

Reveal answer →

1110

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