Thread: Is this sentence wrong ?

This is problem 21 of http://www.du.edu/langlit/russian/genx.htm

У Галины Петровны три хороших мальчика.

I think хороших should be хорошого (maybe хорошего) ??

You've already asked about this. It's correct.

Thank you. I got it now. It is really very tricky!