This is the so-called "viral Vietnamese math problem" that exploded on the internet about a month ago. It was represented as a problem given to 8-yo Vietnamese students, but in my experience, such problems (whatever age they are claimed to be for) are more likely to be 1) math competition problems (e.g. a Math Olympiad open to ages 8-18), a problem some jealous Salieri 3rd grade teacher put on a test to humble a Mozart student (maybe taken from a Math Olympiad) or a problem that is trickier than the original composer realized (just stumbling onto a solution doesn't mean you understood the problem in all its intricacy)

I found what I believe to be the unique solution (that I haven't yet rigorously proven unique), if you interpret the the puzzle as a sequential series of operations rather than interpreting it as a single overall equation (which one can regroup and apply order of operations to). To me, an interpretation with a unique solution is far more compelling interpretation than the approach in the video above, which has been proven by exhaustive computer search to yield 136 solutions.

Taking the problem as a strict sequence of operations (worked backward from the end) turns it into an interesting series of math logic problems leading to (I believe) a unique solution.

The math author who published the above video pointed me to his source: a Vietnamese article by a 3rd grade teacher -- but that articles doesn't claim the teacher was the original author of the problem. I think we can agree (esp. since none of his students found even one of the 136 solutions) that it is really too hard for 3rd grade (or for almost any 3rd grade math teacher to fully apprehend/formulate)

Have fun giving it a twirl under the assumption that it is a sequence of operations, not an equation.

I'll drop hints, if you want/need them

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# The "viral" Vietnamese math problem

Started by
Orpheus
, Jun 27 2015 11:59 PM

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