Question

There are seven fair coins each tossed seven times.The probability of getting atleast 25 heads is?

Answer 1

So it's 49 tosses all together.

Answer 2

\[
\Pr(X\geq 25) = 1 - \Pr(X<25)
\]

Answer 3

In this case it's a binomial distribution.

Answer 4

There are 7 * 7 trials each with P(H) = 0.5.
This can be solved using the binomial distribution and calculating the probabilities of 25, 26, 27,...................47, 48, 49 heads. the results are then added.