On Friday I set this puzzle…

Imagine that the following equation (5 – 2 x 501=802) has been made from matchsticks….

What is the smallest number of matchsticks that can be moved to make it correct? Oh, and you are not allowed to move one to the equation sign to create a ‘not equals to’ sign.

If you have not tried to solve it, have a go now. For everyone else the answer is after the break.

In fact, you don’t have to move any matches. Just hold the equation up to a mirror…..

Did you solve it? Any other answers?

I have produced an ebook containing 101 of the previous Friday Puzzles! It is called PUZZLED and is available for the Kindle (UKhere and USA here) and on the iBookstore (UK here in the USA here). You can try 101 of the puzzles for free here.

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D’Oh! I didn’t think of that. I tried upside-downifying it, which only needed 2 moves; or a “proper” answer, which needed six moves. i gave up too easily.

Good one. Didn’t get it.

Wait…I actually got one? Ha!

To hold the equat up to a mirroe I have to move ALL the matches.

Have you considered moving the mirror instead?

Move mirroe would not be Richards soln. His is “Just hold the equation up to a mirror”

The first one I found was two match stick moves. Turn it upside-down and the change -5 to -2. Another two stick move is change the equals into <, but that is probably not intended to count like making a "not equal to" doesn't count.

I did the upside-down and change 2 matches trick too… didn’t spot this!

There’s also a four stick move to change it to 0 2 X 001 = 002

Great puzzle that required lateral thinking but had no other assumed information about the actual equation or match sticks. A proper puzzle. Pity I didn’t get it.

Not a lot for discussion on this one.

I missed that completely. There are a couple of three stick moves though, if you evaluate left to right instead of evaluating the multiplication first.

an alternative 0 move solution is to read the equation as

S – 2×501 = 802

where S = 1804

hmm… If Richard would have given this answer I would complain…

We will be keeping an eye out for you ctj.

You are the sort of person that is of interest to our organisation.

I did not do the mirror thing. I did the upside down thing:

208 = 105 x 2 – 5

2 matchsticks shifting make it change into:

208 = 105 x 2 – 2

You don’t even need to use ore move a mirror. Put the matchsticks on a glass table, and view it from below.

nice!

Nice, but did`t putting the matches on a glass table require to move them all?

hehehehehe…

I moved a couple of matchsticks for 2 x 401 etc and covered the ‘5 -‘ up with a piece of paper. The solution with the mirror (or glass table) is much better…

I said on Friday that I liked the fact that the puzzle asked for the minimum number of matches instead of giving a target (can you solve the puzzle by moving x matches). I should have realised that the unusual way in which the question was phrased was a clue towards the answer. There is almost always a clue in the question!

Hmmm. Holding up to a mirror doesn’t actually make it correct, it just gives the appearance of being correct. I guess it would be tricky to word this question without giving away the solution though…

Glad I’m not the only “dumb head” here! Lol

you could also just look at it from the side and all you would see is |, which in a Boolean sense is true

Without mirrors and glass tables I got it in 4.

5+7X86=602

Oops that should be 5+2

I don’t know, I’m not really satisfied with this canonical answer – to me, using a mirror doesn’t fulfill “make [this equation] correct”, because you left it unchanged and incorrect – instead, the NEW equation now visible in the mirror is correct.

I stand by invert and move two (which was my original answer as well).

Wouldn’t moving matches be making a new equation too?

Move the two to a 3 (1 stick) so that the left side is 1002

Transform the right side into 1002 by picking up the center match of the 8 and making a (small!) 1 out of it

.. not as elegant as the mirror, ok 🙂

Good one! I’m very glad I didn’t spend much time on this; I’d have never gotten it…

Move four pieces complete away to another place and build there 1=1

I set fire to the matches and smashed the mirror.

On an unrelated note, I rotated the equation 180 degrees and moved the two matches as mentioned above.

Ouch. Please accept my middle finger as gracious thanks, Richard.