Question 1194868
There are 20 balls altogether, and 11 are red.
If a red ball is found it has a 5/11 chance coming from box A
======R========W======Total
A------5-----------4----------9
B------6-----------5---------11
Total--11-----------9---------20
If we select a red ball, it has a 5/11 chance of being from box A.