How to do mysql subquery to get random records from pre-filtered list?

I searched but couldn't find a solution that works. Need a bit help here.

Let's say I have a table with more than 100 records, first, I need to find out top 20 records in certain order, then I need to pick 5 randomly from those 20 records. Here is my query,

SELECT a 
FROM tableA 
WHERE b IN (
    SELECT b 
    FROM tableA 
    WHERE c="x" 
    ORDER BY d DESC 
    LIMIT 20
) 
ORDER BY RAND() 
LIMIT 5;

Let me know how to correct it. Thanks.