Digital design code converter help

[benEE2018]

Homework Statement

design a code converter that converts a decimal digit from the 8 4 -2 -1 code to BCD.

Homework Equations

The Attempt at a Solution

so i listed out the BCD order from 0 to 9 and listed the weighted 8 4 -2 -1 code so that the weights would equal to the BCD equivalent.
8 4 -2 -1--->BCD
ABCD---> WXYZ
0000---> 0000
0111---> 0001
0110---> 0010
0101---> 0011

0100---> 0100
1011---> 0101
1010---> 0110
1001---> 0111

1000---> 1000
1111----> 1001
I then drew 4 K maps for each variable and arrived at an answer that is completely different from the correct answer, W=AB=AC'D'

the answer i got
Z= A'BD+BCD+AB'D
Y=A'BC'D+ A'BCD'+ AB'C'D+ AB'CD'
X= A'BC'D'+ AB'D+ AB'C
W= AB'C'D'+ AB'CD

i don't know what i am doing wrong and any guidance would be greatly appreciated

 

[NascentOxygen]

What converion method have you used to map binary to BCD?

You seem to have written as 1s complement of the BCD, why?