NEW CHALLENGE

Here's a new cadet challenge.  The last two challenges, both pretty tough, were solved by Cadet Ferguson.  This one is fairly simple math--good luck.  Here it is: 

A couple has two children, one of whom is a girl. What is the probability that the other is also a girl? (You may safely assume that the genetic probability of having a baby of either sex is 50%.)

The credited response will include a correct statement as well as a short explanation.  Absolutely no guessing!

Good luck!

Hint:

Two Girls, Pierre-Auguste Renoir, 1892