Poetry in Numbers.. is it 21347!?!?

Question

Write 5 digits in a line all are different none are nine three are odd not so the others each alternates with its brothers twice the first gives you the fourth first plus second equals the third before you write them down too fast third plus fourth gives you the last

Answer 1

Some punctuation would be helpful. But I'll try my best to read it without any.

"Write 5 digits in a line
all are different, none are nine
three are odd, not so the others
each alternates with its brothers"

OK, so there are five digits, three odds (none are 9) and two evens. And they alternate. So they must go: odd - even - odd - even - odd. The odds include three of the following: 1, 3, 5, 7.

"twice the first gives you the fourth"

This means the first is either 1 or 3, because otherwise doubling it doesn't give you a single digit. This also means that the fourth digit is either 2 or 6.

"first plus second equals the third"

The even digits are 0, 2, 4, 6, 8. The second can't be 0, because otherwise the first and third would be the same. Also, we can't have a sum that is 9. So the only possibilities for the first three digits are (1,2,3), (1,4,5), (1,6,7), (3,2,5), (3,4,7). Since the fourth is twice the first this gives (1,2,3,2) (which we can't use, because the 2 repeats), or (1,4,5,2), (1,6,7,2), (3,2,5,6), or (3,4,7,6).

"third plus fourth gives you the last"

The only possibile answer here is (1,2,3,4,7). Adding the third and fourth digit of the other combinations gives you 9 or higher.

Answer 2

I think this violates the "each alternates with its brothers" rule. The first, third and fifth digit should be odd.

Answer 3

Periods and commas were invented for a reason.