5 A pair of fair coins is thrown repeatedly until a pair of tails is obtained. The random variable \(X\) denotes the number of throws required to obtain a pair of tails.
- Find the expected value of \(X\).
- Find the probability that exactly 3 throws are required to obtain a pair of tails.
- Find the probability that fewer than 6 throws are required to obtain a pair of tails.
On a different occasion, a pair of fair coins is thrown 80 times. - Use an approximation to find the probability that a pair of tails is obtained more than 25 times.