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Matchstick Math (Mathematchsticks in the UK version) is a puzzle in Professor Layton and the Unwound Future.

Puzzle

US Version

The math equation below is written in matchsticks! Read as Roman numerals, it means 1 + 11 = 10.

To make this a valid equation, what's the fewest number matches that you need to move?

UK Version

Here's an equation that's been written using matches. Read as Roman numerals, it means: 1 + 11 = 10.

What's the minimum number of matches you need to move to make this equation valid?

Hints




Click a Tab to reveal the Hint.

US Version

Here's a Roman-numeral primer:

I = 1, II = 2, and III = 3.

IIII, however, does not equal four.

IV = 4 and V = 5, so the I in front of the V means one less than five.

VI = 6, VII = 7, and VIII = 8.

IX = 9, X = 10, and XI = 11.

UK Version

Here's a Roman-numeral refresher:

I = 1, II = 2 and III = 3.

IIII, however, does not equal 4.

IV = 4 and V = 5, so the I in front of the V means one less than five.

VI = 6, VII = 7 and VIII = 8.

IX = 9, X = 10 and XI = 11.

US Version

The answer should reveal itself if you understand Hint One and you're willing to look at things from various points of view.

UK Version

The answer should reveal itself if you understand Hint 1 and you're willing to look at things from various points of view.

US Version

As mentioned in Hint Two, it's important to "look at things from various points of view." In other words, don't be afraid to turn this problem on its head...

UK Version

What Hint 2 is basically telling you is to look at things from different directions...

Flip the equation upside down.

US Version

Well, would you look at that! You don't need to move any matches at all. The equation is completely valid as is!

UK Version

Well, would you look at that! You don't need to move any matches at all. The equation is completely valid as it is!


Solution

Incorrect

Too bad!

There's a twist here somewhere...

Correct

You're on fire!

Zero matches is correct.

If you look at the equation upside down, it becomes 10 = 9 + 1 in Roman numerals.

US Version

The phrase "fewest number of matches" might have tricked you into thinking "at least one match," but "fewest" can mean no matches at all!

UK Version

The phrase "minimum number" might have tricked you into thinking "at least one match", but "minimum number" can mean moving no matches at all!

UF148S

A big thanks to http://professorlayton3walkthrough.blogspot.com

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