+23252 Any 5-digit multiply of 12 must be at least 10000.
Because 12 is 4 x 3, any multiply of 12 must be divisible by both 3 and 4.
To be a multiply of 3, the sum of the digits must be divisible by 3.
Since the only digits are either 1 or 0, the number must contain three 1s.
To be divisible by 4, the number must be even, so it must end with a zero; and, since its "twice-even", it must end with two 0s.
11100 fills the requirements...
+23252 Any 5-digit multiply of 12 must be at least 10000.
Because 12 is 4 x 3, any multiply of 12 must be divisible by both 3 and 4.
To be a multiply of 3, the sum of the digits must be divisible by 3.
Since the only digits are either 1 or 0, the number must contain three 1s.
To be divisible by 4, the number must be even, so it must end with a zero; and, since its "twice-even", it must end with two 0s.
11100 fills the requirements...
+118677 Thanks Geno.
I like questions like these.
Many people are capable of trying them , if they are patient enough then they can probably get an answer by themselves, but if they look at your answer as well then they could learn a lot. 
These questions are great for gaining understanding of how numbers 'work'.
