There are two numbers. one number is twice the other number. the difference of the smaller number and half the larger number is 20. an equation created to find the smaller number will have .

If one of the numbers is twice the size of the other number then that number is split in half wouldnt that make the numbers equal? 
for example say the smaller number is 5 and the larger number is 10. 
10 is twice the smaller number, 5. The difference of the smaller number(5) and half of the larger number(10/2) would be 0 in any case. it couldn't come out as 20. 

x=2y
1/2x=y 
x being the larger number and y being the smaller one. 

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