math
posted by victoria .
Assume that the coin is flipped 10 times.
What is the probability that both heads and tails occur?

If you flip 2 coins then 25% chance

P(no heads) = 1/2^10 = 1/1024
P(no tails) = 1/1024
P(no headsno tails) = 1/1024+1/1024 = 1/512
so, 11/512 = 511/512
another way to think of it is that the 1st toss must be identical to the next 9 tosses, so 1/2^9 is the P(next 9 the same)