SEED Science

The Speed of Spiders

Math Puzzles of the Month
The Speed of Spiders

Here are this month’s math puzzles. Actually, this is one puzzle with two variations.

Spider on a wall

Version 1

A spider is climbing slowly up a wall. After one hour it is halfway to the top. After one more hour it covers half the remaining distance, so it is three-quarters of the way to the top. In the next hour it again covers half the remaining distance and is now seven-eighths of the way to the top. If this pattern continues, how long will it take the spider to reach the top of the wall?

Version 2

Now suppose that the spider again climbs halfway to the top in the first hour. But it then covers half the remaining distance in half an hour and is three-quarters of the way to the top in one and a half hours. Then it covers half of the remaining distance in 15 minutes. Again, continuing the pattern, how long will it take to reach the top?

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


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