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This is an exercise from a child's elementary school homework.

A clock takes 6 seconds to strike 4 times at 4:00.
How many seconds will it take to strike 6 times at 6:00?

My logic:

6 seconds/4 strikes = 1.5 second/strike.
1.5 seconds/strike x 6 strikes = 9 seconds.

The author says the answer is 10 seconds.

In the workbook the student is not yet introduced to fractions, so I assume there is another way to solve this.

zundarz
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    Hint: it seems the workbook is counting from after the first chime ends to the end of the last chime. – Macavity Aug 29 '13 at 04:21
  • A somewhat similar question is at:http://math.stackexchange.com/questions/1479029/seconds-of-a-clock?noredirect=1#comment3011689_1479029 – NoChance Oct 14 '15 at 01:13

3 Answers3

10

Let a dash - represent one second. If a clock takes 6 seconds to strike 4 times, then it strikes this pattern:

bong--bong--bong--bong

Continue the pattern to strike 6 times:

bong--bong--bong--bong--bong--bong

Upon counting, there are 10 dashes!

That said, the question is somewhat ambiguous. One suspects that it's an intentional trap, luring the student into a mistake so that they can be taught about fencepost errors.

Chris Culter
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$4$ strikes means there are $3$ intervals between them so $\frac{6}{3}=2$ seconds each (if the strike itself does not take any time).
$6$ strikes means there are $5$ intervals between them so $5\cdot2=10$ seconds in total.
You are correct. No fractions.:)

Caran-d'Ache
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The first bong is striked at exactly $4:00$ pm. The next 3 in the next 6 seconds. So, that 2 seconds per strike.

Again, to strike 6, the first one will go off at exactly $6:00$ pm followed by another 5 strikes, so that's $5\times2=10$ seconds.

Now this is because, if the clock were to strike 4 bongs in 6 seconds, then it should have started at $3:59:54$, so by the time it reaches 4:00 it is complete. But this does not happen, as it will increase the need of calibration in clocks.

MonK
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