Higher November 2021 Paper 3 Q20
20 Pat throws a fair coin \(n\) times.
Find an expression, in terms of \(n\), for the probability that Pat gets at least 1 head and at least 1 tail. (2)
| Answer | Mark | Mark scheme |
|---|---|---|
| \(1 - \left(\dfrac{1}{2}\right)^n - \left(\dfrac{1}{2}\right)^n\) | M1 | for \(\left(\dfrac{1}{2}\right)^n\) oe |
| A1 | oe eg \(1 - \left(\dfrac{1}{2}\right)^{n - 1}\) |