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To Iff or not to Iff?

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In this feature you will find a selection of problems that will require you to reason logically.  You will also be introduced to the symbols $\implies$ and $\iff$ and be challenged to use these to create true statements.

Plus magazine has a selection of interesting articles looking at logic, mathematical logic, its role in computer science and the philosophy of maths, and on how it's being used in applications.

River Crossing
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River crossing

Age
11 to 18
Challenge level
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There is nothing half so much worth doing as simply messing about in boats...
Iffy logic
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Favourite

Iffy logic

Age
14 to 18
Challenge level
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Can you rearrange the cards to make a series of correct mathematical statements?
IFFY triangles
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IFFY triangles

Age
14 to 18
Challenge level
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Can you prove these triangle theorems both ways?

The Tour de Clochemerle
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The Tour de Clochemerle

Age
14 to 18
Challenge level
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Can you work out where these 5 riders came in a not-quite-so-famous bike race?

Iff
problem
Favourite

Iff

Age
14 to 18
Challenge level
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Take a triangular number, multiply it by 8 and add 1. What is special about your answer? Can you prove it?
Mind your \Ps and \Qs
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Mind your Ps and Qs

Age
16 to 18
Challenge level
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Sort these mathematical propositions into a series of 8 correct statements.