Question

if you were to flip a coin 20 times what is the probability you wpuld get exactly 10 heads

Answer 1

Each coin can either land on heads or on tails, 2 choices. 

This gives us a total of 2²⁰ possibilities for flipping 20 coins.

Probability of an event = {Number of ways it can occur} / {Total number of outcomes}

Now how many ways can we get 10 heads? This is 20 choose 10, or $_{20}C_{10}$  

This means our probability is

$_{20}C_{10}/2^{20}=\frac {184756} {1048576}\approx 0.1762$.