Try to see what's going on with the splits of probability.
First flip:
Probability going to heads is [tex]\frac{2}{7}[/tex]
Probability going to tails is [tex]\frac{5}{7}[/tex]
Second flip:
Probability of landing heads twice is [tex]\frac{4}{49}[/tex]
Probability of landing heads and then tails is [tex]\frac{10}{49}[/tex]
Probability of landing tails then heads is [tex]\frac{10}{49}[/tex]
Probability of landing tails twice is [tex]\frac{25}{49}[/tex]
