Question

If you flip a fair coin four times, what is the probability that there you get heads twice?

Answer 1

You can attack this problem in several ways.

Explanation:

Since there are only 16 combinations (2 for the first, times the second, third and fourth) you can write them out:
HHHH, HHHT, HHTH, HHTT, etc.
And filter out the right ones. Divide this by `16`

Or:
You can use the binomial function on your GC.
I use a TI-83 Plus:
2nd-distr -- binompdf(4, 0.5, 2) `=0.375=6/16=3/8`

(This means: 4 tries, chance =0.5, exactly 2 good outcomes)