John has to graph a set of parabolas of the form $y = x^2 - 4x + 2^n$ where $n$ is an integer and $0 ≤ n ≤ 6$. What is the probability that one of these parabolas, chosen at random, will have: 9-78 HW eTool .

1. One $x$-intercept?

2. Two $x$-intercepts?

3. No $x$-intercepts?