h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Here's a practical application

A shop window has a display of children's bricks stacked in a giant cube. Unfortunately, the stack collapses when the cleaner tries to hoover it. After weighing the bricks, we determine there must be exactly 21,952 of them. How many bricks make one side of the giant cube?

OK, not *that* practical.

How can you be sure that some of the bricks didn't get sucked into the hoover? Who's going to go through the dust bag and check?

It's a Dyson, of course

Entry: How to Do Large Cube Roots in Your Head - A85661724
Author: frleon - U14872593


The problem with the party trick aspect is that you will need to get someone to first calculate a perfect cube. But I guess someone who may be impressed by a cube root extraction would also be willing to do so.



Ah yes, so another criticism: you never say where this cube number appears from. You just say, if you are given a large number, *and you know it is a perfect cube*, here is an easy method to extract the cube root.

Now in practise, there is little chance that a random large integer will be a perfect cube, so in effect, you need someone to compute it first and tell you afterwards.

I am still not sure why they should then believe that the number you produce is not simply the result of learning a list of hundred numbers by brute force.

In all fairness it is described as a party trick - not technique to be relied upon by air traffic controllers over Narita Airport at 5:30pm on a Tuesday. So I think we can assume a fair amount of goodwill among the group and a good laugh if it all goes wrong.

In fact if the author made it clear that this is not a mental arithmetic method to be used in high pressure situations but only at parties among consenting participants, then many of the criticisms will be addressed.

Exactly. A few more words about the party aspect would be great. We love parties

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I hope to frleon come back as there are two other of his Entries I'd like to see be selected, they are both very interesting subjects.

Congratulations!


Geggs