Either/Or Clues in Logic Grid Puzzles

Part 2 of 6 of How to Solve Logic Grid Puzzles.

An either/or clue names one item and gives two options for it. Exactly one option is true, and the other is false.

Clue 1. The insect that was auctioned 3rd was either the insect won by Joel or the butterfly that sold for $250.

The item is the 3rd lot. Its two options are "won by Joel" and "sold for $250".

The two options are different things

Exactly one option is true, so Joel's butterfly and the $250 butterfly can't be the same butterfly. If they were, the two options would be true together or false together.

So put an X where Joel meets $250. You can do this before you know anything about the 3rd lot, which makes it an easy X to miss.

Rule out one option and the other is true

Nothing on the grid rules out either option yet, so this is as far as the clue goes for now. Keep it in mind, though. As soon as you learn that the 3rd lot didn't sell for $250, you will know that Joel won it. And if you learn that Joel didn't win it, you will know it sold for $250.

That is how this clue ends up being used, in the last part.

When both options are in the same category

Some either/or clues give two options from one category, such as "The 6th lot sold for either $260 or $270". This kind has no hidden X, because two prices are already different things. Instead, cross out every other price for the 6th lot: $250, $280 and $290.

Practise on puzzles like these in our Logic Grid Puzzles app, for iPhone, iPad, Android and Amazon Fire.

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