Answer :
The ones could be a 1, or 2, or 3, or 4, or 5.
The tens is twice the thousands, so it can't be a 10 (cuz that's not a single digit number) and it can't be a 9 (cuz the thousands digit can't be a 4.5) or a 7 (cuz the thousands digit can't be 3.5) and it can't be a 5 or 3 or 1 for the same reasons.
The tens could be an 8, 6, or 4, or 2. But if the ones digit is half of something and the tens digit is twice that same number, they could be:
ones: 1 or 2
thousands:2 4
tens: 4 8
These are the only two combinations that satisfy all requirements.
And if the thousands digit is 4 greater than the hundreds digit, then the thousands digit can't be 2.
So now do you see?
The tens is twice the thousands, so it can't be a 10 (cuz that's not a single digit number) and it can't be a 9 (cuz the thousands digit can't be a 4.5) or a 7 (cuz the thousands digit can't be 3.5) and it can't be a 5 or 3 or 1 for the same reasons.
The tens could be an 8, 6, or 4, or 2. But if the ones digit is half of something and the tens digit is twice that same number, they could be:
ones: 1 or 2
thousands:2 4
tens: 4 8
These are the only two combinations that satisfy all requirements.
And if the thousands digit is 4 greater than the hundreds digit, then the thousands digit can't be 2.
So now do you see?