Question

Let X, the number of tails in three flips, assign a value to each element in the sample space: {HHH,HHT,HTT, TTT, THH, TTH, HTH, THT\} For example, X(HTT)=2. X(HTT)=2. Since fair coin flips are unpredictable, X is a random variable. Calculate P(X=2) 1/4 1 1/2 3/8

Answer 1

Answer: 3/8

Reason:

X = 2 corresponds to having two tails show up in any order.

The event space for two tails is:

• HTT
• THT
• TTH

We have 3 ways to get what we want out of 8 items in the sample space. That's how we arrive at 3/8