Probability

First, let's find the total number of cases we work through. We can actually just list them all out. 

We have

$(HHT,HTH,HTT, THH, THT, TTH, TTT)$

The only possibility where a head doesn't appear is TTT. That means that

$(HHT,HTH,HTT, THH, THT, TTH)$ all work. 

Since probability is essentially $\text{Probability} = \frac{\text{# of Favorable Outcomes}}{\text{Total Outcomes}}$

So we just have $\frac{6}{7}$

So 6/7 is our answer. 

Thanks! :)