# Is It Straight?

## Math Puzzles of the Month Is It Straight?

What is the best way to hang the mirror so it is straight? Find out from this puzzle.

Mitchell hung a mirror on the wall in his house.

To make sure it was perfectly straight, he measured exactly 40 cm (16 in) from each of two points along the left edge of the mirror to the adjoining wall. But when his wife Luanne walked in and looked at the job, she said, "It's not straight."

"That can't be," said Mitchell. "I know these walls are vertical because I double checked them with a level and with a plumb line. I measured from the left edge of the mirror to the wall in two places, both 40 cm. And I also checked to make sure that the mirror is a perfect rectangle. The wall is vertical. The left edge of the mirror is parallel to the wall. The right edge of the mirror is parallel to the left edge. It's straight."

"Well," said Luanne, "I'm looking at the right edge of the mirror, and it isn't vertical."

Who's right, Mitchell or Luanne?

After you've tried this for yourself, check our solution.