Three girls

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We will use the choice function from the random module.

>>> import random

This is a module:

>>> type(random)
<class 'module'>

Use random. and then Tab to see the functions inside the module, from within the Notebook.

We will use random.choice, a function within the random module.

You can check the help with random.choice? in the Notebook.

Here we ask it to choose randomly between the two letters in the string, "HT":

>>> random.choice('HT')
'H'
>>> random.choice('HT')
'T'
>>> random.choice('HT')
'H'
>>> random.choice('HT')
'H'

A coin toss!

Now we have everything we need to solve the problem:

>>> # Make list to store counts of girls in each family
>>> girl_counts = []

>>> # Make 10000 families
>>> for i in range(10000):
...     # Make one family
...     family = []
...     # Have 4 children
...     for j in range(4):
...         child = random.choice('GB')
...         family.append(child)
...     # Store the number of girls in this family
...     n_girls = family.count('G')
...     girl_counts.append(n_girls)
...
>>> # Get the number of families with 3 girls
>>> n_with_3 = girl_counts.count(3)
>>> proportion = n_with_3 / 10000

>>> proportion
0.2548