Tuesday, 30 April 2013

The Counterfeit Coin

The Counterfeit Coin

by Rick Lime

So this week when the rhyme word is hum
And I’ve o’er used ‘cum’,  ‘dum’, ‘thumb’, and ‘bum’
A conundrum I’ll pose
Will you solve it, who knows?
I suspect though, it’s too tough for some

Now the gears in my head start to hum
As the clues for this puzzle forth come
You’ve got 12 coins of gold
But there’s one that is old
It’s weight’s off from the rest, by a crumb

You’ve a scale (not of music to hum)
It’s two pans on a chain, and it’s plumb
With this scale weigh the gold
‘Till at last you behold
The coin others are different from

If at this point you’re all thinking hummm ….
Here’s a clue to begin, don’t be glum
Place some coins in each pan
If they balance you can
Safely say that it’s not in that scrum

Since you now see this isn’t ho-hum
One more thing, please don’t think I’m a bum
The odd coin may be light
Or just overweight, slight
And three weighing’s the goal, good luck chum


  1. Thanks so much for your fun and fascinating contribution to this week's Limerick-Off!

  2. In the following, H stands for suspected heavy, L for suspected light.

    The first step is checking the weight
    Of four against four on each plate.
    That narrows it down
    To four (weight unknown)
    Or four “H” and four “L” which makes eight.

    In the former case, weigh any three
    Of the suspects with 3 known to be
    Standard weight; this will tell
    If the group’s “H” or “L”
    And from there it’s not hard, you’ll agree.

    In the latter case, one must reduce
    The 8 suspects to 3 or a deuce
    One set of which hold
    The one that is old -
    A solvable group to produce.

    So you load two “H” coins and a “Light”
    On each side, the left and the right,
    If one side weighs bigger
    That helps you to figure
    Three coins (or two spare “L”s) to fight.

    If now down to three, and you know
    Which way each is suspected to go
    You just pick a pair
    That might match, weigh them; there
    Is your answer. (I *think* this is so.)