Puzzles from the Math Midway
The Missing-Mark 12-inch Ruler:
Here's what Sally came up with: Put marks at 1 inches, 3 inches, 7 inches, and 11 inches. Then:
| To measure |
Measure from: |
and measure to: |
| 1 inch |
left end of ruler |
1-inch mark |
| 2 inches |
1-inch mark |
3-inch mark |
| 3 inches |
left end of ruler |
3-inch mark |
| 4 inches |
3-inch mark |
7-inch mark |
| 5 inches |
7-inch mark |
right end of ruler |
| 6 inches |
1-inch mark |
7-inch mark |
| 7 inches |
left end of ruler |
7-inch mark |
| 8 inches |
3-inch mark |
11-inch mark |
| 9 inches |
3-inch mark |
right end of ruler |
| 10 inches |
1-inch mark |
11-inch mark |
| 11 inches |
left end of ruler |
11-inch mark |
| 12 inches |
left end of ruler |
right end of ruler |
There are lots of fun problems like this. For a big challenge, try to find the fewest number of marks you can put on a yardstick to be able to measure any length from 1 to 36 inches.
Get answers to these puzzles: