Let's assume x be the number.
Given that, one number is twice the other number. Hence, the second number be 2x.
So, x= smaller number and 2x= larger number.
Given that, difference of x and half of 2x is 20. Hence,
x-x=20 (By simplifying)
0=20
From the above result we can see that x has vanish and we are left with 0=20 which is mathematically not correct.
Hence, there is no solution.