Monday, September 08, 2008

digital puzzle!

(solution provided at the bottom of this post)

this is a logical puzzle that struck me when i was waiting at one of those traffic signals which take inordinately long to turn green!

some of the signals mercifully have a digital counter which counts down the seconds between the signal color changes. and as i watched, i noticed that one of the digital digits was showing me a weird set of numerals as it was counting down. it was obviously because one of the 7 (3 horizontal and 4 vertical lines) lines of the figure 8 was not working.

this got me thinking up this particular problem -

which of the 7 lines of the figure 8, if it was not working, would still cause the counter to display the longest sequence of valid numerals, albeit not in logical order? (irrespective of whether the counter was counting up or down)

options -
1. top horizontal
2. middle horizontal
3. bottom horizontal
4. top-left vertical
5. bottom-left vertical
6. top-right vertical
7. bottom-right vertical

also list the sequence of valid numerals.

(p.s. you can send in your answers as comments or by email. the contest closes at 12 mid-night IST on 14th sept 2008)

p.s. in case you like such logical puzzles, click here to check out the previous one!


quite a few people got the answer correctly... though some of them interpreted the problem a little differently...

the correct answer is option 5, the bottom-left vertical segment.

if this segment is defective then the longest sequence of valid numerals that result are - 3, 4, 5, 5 (instead of 6), 7, 9 (instead of 8) and 9!

i have posted all the comments received so far! manasi ( was the first respondent with the correct answer! :)



Manasi said...

Very interesting Guru!!! It goes on to prove that nerds like me are not entirely alone in this big bad world :-D

From your list, my money is on # 5. bottom-left vertical

Reasoning: the Count of numerals unaffected by the removal of -->

1. top horizontal = 2
2. middle horizontal = 2
3. bottom horizontal = 3
4. top-left vertical = 4
5. bottom-left vertical = 5 <--
6. top-right vertical = 2
7. bottom-right vertical = 1

Thus, the bottom left vertical is the only one whose removal leaves the max numerals unaffected i.e. - 1, 3, 4, 5, 7 ensuring the "longest sequence of valid numerals, albeit not in logical order"



Nibedita said...

This is so kool!!!..
If I understood the question right then surely the answer is:
the bottom left vertical line.
the numericals: 3, 4, 5, 7, 9

Anonymous said...

top right vertical? Coz' that would form a 6....

Anonymous said...

1. top horizontal 1 4
2. middle horizontal 1 7 0
3. bottom horizontal 1 4 7
4. top-left vertical 1 2 3 7
5. bottom-left vertical 1 3 5 7 9
6. top-right vertical 5 6
7. bottom-right vertical 2

The answer shud be 5. On the contrary, the manufacturer of such equipment should provide some sort of backup for option 7, because thats what is the most critical link

Balaji said...

Leaving out:
the top-left vertical - 1,2,3 would still be valid
the bottom-left vertical - 3,4,5 would be valid

Apart from these two, there's no longer sequence possible.

mathatheist said...

Bottom Left vertical?

Anand Ramachandran said...

Hi Guru, Extremely good question. The answer is "Bottom Left Vertical" since that line figures only at four places- 0,2,6 and 8.The other lines figure more than four times in the numerals.

Warm regards
Anand Ramachandran

Anonymous said...


I think bottom left vertical not working will still have 1,3,4,5,7,9 display correctly.

If in logical order, top left vertical, though not working will cause 1, 2, 3 display correctly.


Best Regards,

Vibha Ramakrishna

Anonymous said...

ur unbelievable!! hehehe i don't think i've ever managed to think of thinking anything constructive at a signal.......

anyway my answer is bottom left verticle i.e. option 5

Anonymous said...

Bottom-left vertical. It will display 1, 3, 4, 5, 7, 9.

Any of the horizontal ones don't make any sense because they will deprive you of 0, 2, 3, 4, 5, 6, 7, 9 depending on which one you remove.

Top-right vertical or bottom-right vertical will deprive you of 1, 2, 3, 4, 7, 9 or 1, 2, 3, 5, 6, 7, 9 respectively.

Top-left vertical was my first choice but it only gives you 1, 2, 3, 7.

I haven't included 8 at all in any of the options because it requires all the numbers.

Also, if you remove the middle horizontal, you can still display 0, 1, 7 but no other numbers because they all have the middle horizontal.
Am I right? :D

Achintya Rao
P. S. It took my about 15 seconds to figure this out. So, if I AM wrong, then it means I've to give this kinda thing a lot more thought. :P

Anonymous said...

Bottom left verticle

ajit sukhatankar

Guruprasad said...

hi all :

i have added the solution at the bottom of this same post... do check it out.


p.s. and thanks for writing in! :)

Tys on Ice said...

must be the alcohol...but i kinda tuned off when u started mentioning numbers...


btw, next time u r stuck at a red light, just surf the radio channels..

Manasi said...

you've been awarded!!! check my space...