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# Can you figure this out, within 5 minutes?

9 replies to this topic

### #1 Panda_ca

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Posted 21 December 2007 - 02:22 PM

Draw a 4 by 4 matrix so as to display 4 columns and 4
rows. In the top row, place the number 999 in the first box, then follow with
the number 998 in the second box. The number 997 is placed in the third box and
the number 996 goes in the fourth box.

Second row down, has the numbers 729, 648, 567 and 486 placed in each box of
that row.

Third row, second to the bottom row, has the numbers 126, 192, 210 and 192
placed in each box of that row.

The bottom row, has the numbers 12, 18, ? ,and 18 placed each box.

Note: The matrix dimensions must appear as follows.

999, 998, 997, 996

729, 648, 567, 486

126, 192, 210, 192

12, 18, ?, 18

Find the missing number, i.e., ?
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### #2 tivoli

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Posted 21 December 2007 - 05:02 PM

No, I could not
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### #3 Writersblock

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Posted 21 December 2007 - 05:53 PM

1 min 15 seconds (if I'm right).

No vertical relationships. Top row decline by 1. Second row alternating digits decrease & increase. Seems like the horizontal relationships are independant from the others.

I'd guess that the missing number is 12
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### #4 hipowertech

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Posted 21 December 2007 - 06:32 PM

Draw a 4 by 4 matrix so as to display 4 columns and 4
rows. In the top row, place the number 999 in the first box, then follow with
the number 998 in the second box. The number 997 is placed in the third box and
the number 996 goes in the fourth box.

Second row down, has the numbers 729, 648, 567 and 486 placed in each box of
that row.

Third row, second to the bottom row, has the numbers 126, 192, 210 and 192
placed in each box of that row.

The bottom row, has the numbers 12, 18, ? ,and 18 placed each box.

Note: The matrix dimensions must appear as follows.

999, 998, 997, 996

729, 648, 567, 486

126, 192, 210, 192

12, 18, ?, 18

Find the missing number, i.e., ?

looking at the third row I see that the second digit multiplied by the third digit equals the number in the same column of the fourth row. If this is the next step in the problem then the answer would be zero. I'm still lining up the other steps that got us from the second to the third row, but I think Im close, If my answer is right then 2.5 mins appx.
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### #5 spoxjox

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Posted 21 December 2007 - 07:00 PM

Draw a 4 by 4 matrix so as to display 4 columns and 4
rows. In the top row, place the number 999 in the first box, then follow with
the number 998 in the second box. The number 997 is placed in the third box and
the number 996 goes in the fourth box.

Second row down, has the numbers 729, 648, 567 and 486 placed in each box of
that row.

Third row, second to the bottom row, has the numbers 126, 192, 210 and 192
placed in each box of that row.

The bottom row, has the numbers 12, 18, ? ,and 18 placed each box.

Note: The matrix dimensions must appear as follows.

999, 998, 997, 996

729, 648, 567, 486

126, 192, 210, 192

12, 18, ?, 18

Find the missing number, i.e., ?

2. Each number is equal to the product of the digits of the number immediately above it. (It was "729" that tipped me off, which is a perfect cube of 9. With "999" above it, that sort of gave it away...took about 30 seconds. It's really a question of how long it takes to stumble across the answer, which could be fast or could take a long time. Even the same person could get widely varying results if trying the problem at various times.)
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### #6 undeniable

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Posted 21 December 2007 - 08:26 PM

0
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### #7 spoxjox

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Posted 21 December 2007 - 08:51 PM

0

Excellent point. I was ignoring all zeros, both leading and trailing, since otherwise any product would be zero. But if you made the case that nontrivial zeros should be counted, then you are right, the answer would be 0, not 2.
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### #8 Writersblock

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Posted 21 December 2007 - 09:08 PM

Nice one. Missed that completely. Need to spend more time on math.
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### #9 hipowertech

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Posted 21 December 2007 - 10:46 PM

well, I got the right answer but for the wrong reasons. So, in the show your work category of the math test I got a score of zero. Kind of ironic since the answer was also zero.
good one, both to panda for the riddle and spox for the answer.

Peace.
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### #10 Panda_ca

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Posted 30 December 2007 - 02:21 PM

Wow great job guys! I was expecting this brain teaser to go on for a bit longer. Looks like there is some real brain hp around here.
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