Phil Mahler
Middlesex CC
Bedford, MA
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Part 1
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I was cleaning out old newspaper clippings and came across two old items in
Marilyn Vos Savant's column, in "Parade Magazine." Thought they might be of
interest - in fact they might make good student group projects at the
appropriate levels (a few years ago I would have said good extra credit
problems :-) ).
1. Where can I find a table that shows how long it takes to double my
money at various interest rates? (May 3, 1992)
You don't really need a table. For a good approximation, just divide
72 by the interest-rate number (use 5 for .05), and the answer is
the number of years it wil ltake your money to double. For example, at
4.5%, it takes 16 years (72 / 4.5 = 16).
(Question: Why does this work? How good is it?)
2. You have a solid sphere and bore a perfect hole through the center of
it. This leaves a cylindrical hole that is 6 inches long. What is the
volume of the remainder of the sphere? (October 20, 1996)
(I won't give Ms. Vos Savant's answer. I haven't tried it myself,
but the answer is surprising.)
Part 2
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Nothing to so with math. It drives me crazy to write something like
in "Parade Magazine."
where the period is before the second quote. I'm told that this is proper
usage, but that in England they do it the "right" way, before the period.
Part 3
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A true anecdote, related by some friends, who are not math educators. It
is about their niece, who is 6. I'll call her Mary - obviously a budding
mathematician.
Mary was asked by her mother to help with the dishes, and dry ten items
in the dishrack. She responded that she couldn't count to ten. Her mother
replied that Mary's teacher said Mary could count to 100.
Yes, Mary said, but I start at eleven.
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