Permutation and Combination Help!

**Question:**

A coin is tossed 10 times.

(a) How many different sequences of heads and tails are possible?

(b) How many different sequences containing six heads and four tails are possible?

(c) What is the probability of getting si heads and four tails?

**Attempt:**

(a) = 0 Heads or 1 Heads or 2 Heads or 3 Heads or 4 Heads or 5 Heads or 6 Heads or 7 Heads or 8 Heads or 9 Heads or 10 Heads.

$\displaystyle = 10C0 + 10C1 + 10C2 + 10C3 + 10C4 + 10C5 + 10C6 + 10C7 + 10C8 + 10C9 + 10C10$

$\displaystyle = 1024$

(b) $\displaystyle = 10C6+10C4 = 420$

(c) No Idea!