Bowls X and Y each contained exactly 2 jelly beans, each of

[BTGmoderatorDC]

Bowls X and Y each contained exactly 2 jelly beans, each of which was either red or black. One of the jelly beans in bowl X was exchanged with one of the jelly beans in bowl Y. After the exchange, were both of the jelly beans in bowl X black?

(1) Before the exchange, bowl X contained 2 black jelly beans.
(2) After the exchange, bowl Y contained 1 jelly bean of each color.


OA E

Source: Official Guide

[nitink]

It cannot be (1) alone because before exchange X=BB with Y=RR and Y=BR give different results for X
It cannot be (2) alone because after exchange Y=BR can come from X= BB with Y=RR and Y=BR and can give different results for X
It cannot be (1) and (2) together also because before exchange X=BB with Y=RR and Y=BR can give different results for X with Y=BR after exchange

Answer : E

We should try to use the same counter example as far as possible.