How Old Is Ann?
quuxplusone.github.io28 points by ibobev 2 hours ago
28 points by ibobev 2 hours ago
Rephrasing it makes it easier to grasp:
Mary is 24 years old. When Mary was Ann’s current age, Ann was 12 years old (half Mary’s current age).
This makes it a bit easier to realize that Ann’s age has to be right in the middle of 12 and 24.
"Any eighth-grade boy or girl who is 'all there' should solve it in about thirty seconds" is hyperbole (it took me a couple of minutes), but in general the public reaction to this seems like a demonstration of the Flynn effect.
> it took me a couple of minutes
Are you in the 8th grade? Those of us a couple of decades past the 8th grade are maybe slower at algebra than someone who is actively drilling it...
Mary IS 24. So Ann WAS 12. Say that was X years ago. Then Mary WAS 24-X and Ann IS 12+X. So 24-X=12+X, X=6, Ann is 18.
I can't see a way to do it without algebra.
> I can't see a way to do it without algebra.
This is related to "When all you have is a hammer, everything looks like a nail."
It's slightly different, because you've supercharged your hammer. Everything you ever understood about how to solve word problems has been subsumed into what your brain labels as "algebra."
But look at it this way:
1) Did you use algebra to convert the problem to algebraic form? Probably not; algebra says nothing about word problems.
2) Once it was in algebraic form, did you need to repeatedly apply algebraic rules in order to reduce the problem, or could you glance at it and figure it out?
there's 12 years between 12 and 24. it is divided equally between OldAnn-OldMary and OldMary-NowMary. 12/2=6, 12+6=18
Wait so how old is she?
what the true answer? oh, there is no? My intuition says that Ann now is 24
This has flashbacks to GMAT problems.
Opus says Ann is 18
Sounds about right.
How I understand it:
Mary is 24, Ann is a few (n) years younger
M = 24
A = M-n
M-2n = M/2 = 12
M-2n = 12 --> n=6
mine was not so parsimonious, my teachers would probably say i am not very clever but has points for effort.
ann_old=12
mary_curr=24
mary_old=ann_curr
mary_curr-ann_curr=X
mary_old-ann_old=X
24-ann_curr=X
mary_old-12=X
ann_curr-12=X
24-ann_curr=ann_curr-12
2ann_curr -12 = 24
2ann_curr = 36
ann_curr = 18