What is a necessary step for constructing perpendicular lines through a point off the line? Draw a line that intersects the first line at an acute angle using a straightedge.
Draw a ray that intersects the first line at an acute angle using a straightedge.
Draw arcs on either side of a given point on the line.
Draw arcs on the given line in two places.

Assume that there is a 11% rate of disk drive failure in a year. a. if all your computer data is stored on a hard disk drive with a copy stored on a second hard disk drive, what is the probability that during a year, you can avoid catastrophe with at least one working drive? b. if copies of all your computer data are stored on four independent hard disk drives, what is the probability that during a year, you can avoid catastrophe with at least one working drive?