Ok I need all you math genuises

[Lindagerr]

This problem was posted on LinkedIn by a friend

9=72
8=56
7=42
6=30
5=20
3=??

Many PhD's and other "Smart" people are disagreeing over the answer. What do you think and why?

[topdog98]

6

x times x-1

3 times 2 = 6

[Daithi]

The next progression after 5=20 is 4=12, but they skipped this number and asked for 3=?. Had they shown 4=12 then 3=6 would be the answer. However, I have no idea how you have a progression that goes 9, 8, 7, 6, 5, 3 with a corresponding progression of 72, 56, 42, 30, 20, ?. If you show the 4 in the progression with the corresponding 12 then everything is fine, but if you don't then some other pattern may be at play. Once possible pattern is--

x = x - (10 \ x) this gives the progression 9, 8, 7, 6, 5, 3

the other side of the equal sign uses a corresponding progression of--

x = (x - (10 \ x )) * (x - (10 \ x ) - (10 \ x)) this gives the progression 72, 56, 42, 30, 20, 3

So, the answer is 3

[Sterling Archer]

I'm no genius, but I believe the answer is 15

[cookderosa]

do you want fries with that? LOL I have no clue!

[Lindagerr]

Well after 10 days the "experts are still not decided. answers go from 27-3 everyone is sure there answer is right and most can even give a good example of why they are right. I will let you know if there is ever a strong consensus.

BTW my answer is 6, but I am by no means a math expert.

@Sterling how do you arrive at your answer? I like to see everyone's reasoning.

[cookderosa]

Well after 10 days the "experts are still not decided. answers go from 27-3 everyone is sure there answer is right and most can even give a good example of why they are right. I will let you know if there is ever a strong consensus.

BTW my answer is 6, but I am by no means a math expert.

@Sterling how do you arrive at your answer? I like to see everyone's reasoning.

Linda you should mail it into the genius who has her column in the Sunday insert. She solves all kinds of riddles and problems sent in by readers!

[Lindagerr]

Jennifer I know some of the people who have answered on the linked in page many of them are math, science or engineering PhD's. I think this is more like a brain teaser there is not one answer it all depends on what equation or progression you use. I have now seen 3 that make perfect sense but come up with different answers (Including Daithi's that is a good one). So I am just waiting until the friend that posted it gives an answer. Then I will kill her for driving us all nuts LOLbanghead

[Lindagerr]

Well after hundreds of post on linked in the majority seem to feel the answer is 6.

we have

12 + 8= 20 + 10 = 30 + 12= 42 + 14 = 56 + 16 = 72 Ergo 6

9*8=72 8*7=56 7*6=42 6*5=30 5*4=20 and finally 3*2=6.

3 = 6 = 30. Explanation: 6 = 30 (6*5) 5 = 20 (5*4) 4 = 12 (4*3) 3 = 6 (3*2). Above 6 = 30. So, 3 = 6 = 30 ???? I don't get this one

Ans could be =13. Ex: Focus on 7 and 6 equations. (7+6)-1 = 12. Substract 12 from 42 you get 30! So in case of 5 and 3, [20 - (5+3-1)] = 13!

3=12 , 1+2=3 then 3=3 so answer is 12

3 =12. here is the explanation.9*8=72, 8*7=56, 7*6=42, 6*5=30, 5*4=20 and now, 4*3=12. This gives 3 the answer of 12.

There are many possibilities to solve: 3=3 3=1x3 3=2+1 3=3-0 3=100-97 ... and all other equations on top are mathematically wrong no matter which base system you are using.

Oh my God! 56=72 - 8x2 42=56 - 7x2 30=42 - 6x2 20=30 - 5x2 14 (the correct answer) =20 - 3x2 It's very easy!!

Answer is 6 as per the pattern (axa)-a = b, e.g. as per patterns 9X9-9=72,8X8-8=56,7X7-7=42,6X6-6=30,5X5-5=20, So 3X3-3 = 6.. Hope it clarifies.



I find it interesting that there are smart people from all over the world in all walks of life who can not agree on an answer. Several people have also come up with 15 as an answer but no one has explained how. It turns out my friend is not the original poster so I don't know if I will ever find out if there is a definitive answer. I like answers this frustrates me.

[anonymouse]

This is a cool thread.

My initial answer was 6 for the same reason as topdog98's. Though, since it skips 4, there is probably something else going on.

Maybe there is no definite answer for this problem-- not enough facts given for a conclusive answer.