Ummm what day was it, a matchstick puzzle

Question

      XXIII  
     -------  =  II  
       VII

All you need to do is move one matchstick from the roman numerals to make the equation true.

I remember this one from when I was a kid (40 odd years ago), great seeing it here! — Abel, Feb 13 '22 at 21:23

score 19 · Accepted Answer · edited Mar 15 '16 at 19:12

19

You could move...

The last I from the numerator onto the top of the result, like so:

XXII
---- = $\pi$
VII
It's an approximation, but yesterday was Pi Day.

edited Mar 15 '16 at 19:12

ABcDexter

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answered Mar 15 '16 at 19:02

question_asker

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Absolutely correct. Both the reasoning and the answer ^_^ – ABcDexter Mar 15 '16 at 19:14
So "yesterday" is close enough? When is the cutoff that this answer would no longer be appropriate? :P – TTT Mar 15 '16 at 20:04
1

@ttt it will always be yesterday relative to the posting of the question – question_asker Mar 15 '16 at 20:05
1

@question_asker, I meant, if this question was asked 6 months from now, I don't think the answer would be correct since 22/7 does not equal pi. (6 months from now you wouldn't say, 22/7 = pi and pi day is March 14. At least I don't think I would say that...) – TTT Mar 15 '16 at 20:09
1

@ttt but the question isn't posted six months from now, it was posted today – question_asker Mar 15 '16 at 20:18
@question_asker - I know that. But for fun, I'm just wondering when the cutoff would be. I think tomorrow would be fine, maybe even the next day or any day this week. Next month, probably not. Can you draw a line in the sand and say, "This is a good answer if the question is asked within X days of pi day." I wonder what X is. – TTT Mar 15 '16 at 20:38
@ttt I get what you're saying but I think the answer is that any day is a good day as long as you incorporate [integral part of the answer] into the question somehow. It doesn't have to be about the day – question_asker Mar 15 '16 at 20:40
2

@TTT "Yesterday" will always be assumed to be "yesterday at the time of writing" (equal to the day before the post was written), and since these posts are all timestamped, there's no problem. – jpmc26 Mar 15 '16 at 23:07
@jpmc26, I must be explaining this poorly. I'm just curious about a psychological experiment. How far from pi day could this question have been asked so that it would still be considered a good question? I'm suggesting the answer might be about 3-5 days... – TTT Mar 16 '16 at 14:12
@TTT Do you want the question to be renamed as "What day was it yesterday" :-P – ABcDexter Mar 16 '16 at 14:55
1

@ABcDexter Please let's not. Though there is a fair point here somewhere about the possibility of leaving the relative date out entirely and otherwise obliquely hinting at it. – question_asker Mar 16 '16 at 14:56
1

@question_asker, Yes exactly. That is why I didn't do it at the first place. And by the way, this question was asked in a puzzling competition here :-) – ABcDexter Mar 16 '16 at 14:58
1

@ABcDexter - if you renamed the question it would have been far too easy! I like it the way you have it. – TTT Mar 16 '16 at 15:28
Yesterday could also be acceptable on July 23, (which, in Europe, at least, would be 22/7). – Matt Mar 18 '16 at 01:18
Works fine for today ^-^ – ABcDexter Mar 14 '17 at 15:38

score 17 · Answer 2 · edited Apr 13 '17 at 12:50

17

If in “make the equation true” only the words make and true are taken literally:

XXII
—— &hairsp; ≠ &hairsp; II
&hairsp; VII

As quintopia points out, this is no longer an equation. (A deserved custard $\pi$ in my face.)

edited Apr 13 '17 at 12:50

Community

1

answered Mar 15 '16 at 19:09

humn

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Well, that would go into the lateral-thinking part ;-) – ABcDexter Mar 15 '16 at 19:15
Hahahahahaha. Well played! – Khale_Kitha Mar 15 '16 at 22:46
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Is an inequality considered a equation? – quintopia Mar 17 '16 at 17:53
Too true, @quintopia, the answer now includes a duly credited disclaimer. (As a matter of fact, to make the original equation true would require, more than moving a match, redefining the symbols used.) – humn Mar 17 '16 at 21:39

goodguy5 · Answer 3 · 2016-03-15T19:31:25.333

12

I think I'm allowed to:

X\III
------ = II
VII
It's hard to tell, but I removed part of an 'X' to make a single piece (placing the spare piece in the division sign), showing an informal "14". 14 divided by 7 equals 2.

shrug "proof"

"XXIII" is 23 and consists of 7 "sticks", where each "X" is two sticks. The division sign is made of 5 sticks (possibly just a coincidence, but "meh"). The "VII" is 7 and consists of 4 "sticks, where each "V" is represented by two sticks.

Remove one stick from the second X in "XXIII" to create "XIIII" (7-1 sticks) and place that stick in the division sign (which now consists of 5+1 sticks).

edited Mar 15 '16 at 19:31

answered Mar 15 '16 at 19:12

goodguy5

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But you moved two matchsticks! – ABcDexter Mar 15 '16 at 19:15
@ABcDexter how? I moved half of the 'X' (which consists of two matches). Unless I copied it wrong, which is possible. – goodguy5 Mar 15 '16 at 19:17
This was actually my first thought, and the reason I asked the question I did in the comments – question_asker Mar 15 '16 at 19:20
1

Where did the I of the 23 go? You placed the spare piece in the division sign right. – ABcDexter Mar 15 '16 at 19:21
@ABcDexter yes. the "spare" piece is in the division sign (which is composed of several "sticks" in your example). That leaves an 'X' and four 'I's, though, one of them is a bit crooked. – goodguy5 Mar 15 '16 at 19:23
Ok, but again, you needed to move exactly one stick :-) – ABcDexter Mar 15 '16 at 19:25
1

@ABcDexter. (this textblock reads aggressively and that is not what I was going for) Am I typing what I'm trying to say wrong? Can someone please chime in? I'll try one more time to explain what I'm saying: please see the edit. – goodguy5 Mar 15 '16 at 19:31
@goodguy5 Ok, understood and upvoted. – ABcDexter Mar 16 '16 at 05:06

score 6 · Answer 4 · answered Mar 15 '16 at 21:16

XXIII
----- = II
VII

can be changed to become...

XXIII
----- > II
VII

in which...

I slightly move one of the sticks in the equals sign to become a greater-than sign. Because I cannot visually represent it, the top line will be angled downward to meet its bottom compatriot. Like so, but reversed: ∠

Ummm what day was it, a matchstick puzzle

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