A couple has three children. Suppose the birth of boys and girls is equally likely, let X be the number of girls among the children. Determine the values of X and find the probability distribution of the number of girls X. Use the probability distribution to find:
1. The mean or expected number of girls among the three children.
I got 0.75. It was incorrect.
2. The variance of the number of girls X among the three children.
I got 0.69. It was incorrect.
3. The standard deviation of the number of girls X.
I got 0.83. It was incorrect.