Given the sentence "A group of girls in red gowns are in the middle of a musical performance." is it true that "Three girls are wearing red ball gowns in the senior class play."?
Let's be accurate as possible and think first.
it is not possible to tell
A group does not have to be three people.

And a musical performance does not have to be the senior class play.

It could be a musical performance put on by anyone.

.

So, the final answer is it is not possible to tell