6 of 6 Items .... Source: Gabriel Rosenberg

Problems, Questions, and Puzzles to spark discussion and argument in the maths classroom.

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From Gabriel Rosenberg via email

True or False?

If my stock increases in value by 28% one year, and then decreased in value by 2% the following year, then on average it increased by 13% per year.

If I powerwalk to school at a constant speed of 4 miles per hour, and then saunter home at a constant speed of 2 miles per hour, then I averaged 3 miles per hour for my trip.


.: [PREALG], [Gabriel Rosenberg], [Understandings].

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True or False?

Two-thirds and four-sixths are the same number.

What if we know about complex numbers?


.: [ALL], [Gabriel Rosenberg], [Number Theory].

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We all know that \(\sqrt{4*4} = 4\) and \(\sqrt{3*3} = 3\). We know that \(\sqrt{12.4*12.4} =12.4\).

What's \(\sqrt{-4*-4} = ? \)

Which is it ... or both?


.: [ALL], [Gabriel Rosenberg], [Number Theory].

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When I ask "How many numbers are there?", I get the usual "An infinite number!"

  • If there are the same number of positive numbers and negative numbers, is the number of positive numbers (\(\infty)\) - the number of negative numbers (also \(\infty\)) = 0?



.: [ALL], [Gabriel Rosenberg], [Number Theory].

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True or False?

\(\infty\) is a number.
\(\infty\) can be negative.
\(\infty - \infty = 0\)
\(0 * \infty= 0\)
\(\infty \div \infty = 1\)


.: [ALL], [Gabriel Rosenberg], [Number Theory].

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True or False?


A line is parallel to itself.


.: [GEOM], [Gabriel Rosenberg], [Understandings].
that's it.