Regifting Robin

This math puzzle has been sent to me in the past few years by a number of people:

It appears that Robin can read your mind! Right over the internet! Amazing!

But not really, as it’s based on a simple mathematical trick.

See if you can figure out the mathematical trick before you search for the solution, which is probably all over the internet. (As usual, it’s the struggle to solve the problem that develops your mind; even if you don’t solve the problem, striving to do so prepares your mind so that you will better understand and remember the solution even if you have to look it up.)

Have fun!


About Santo D'Agostino

I have taught mathematics and physics since the mid 1980s. I have also been a textbook writer/editor since then. Currently I am working independently on a number of writing and education projects while teaching physics at my local university. I love math and physics, and love teaching and writing about them. My blog also discusses education, science, environment, etc. Further resources, and online tutoring, can be found at my other site
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