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How old is Ann?

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Re: How old is Ann?

#21

Post by skipants »

zephen wrote: post #17
tempfile wrote: post #13

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…

Uhhh... what? The OP is right; even if you do it intuitively it's still algebra. If you need a proverb to justify it: Just because your hammer is made of stone doesn't make it less of a hammer.

Re: How old is Ann?

#22

Post by Jtarii »

swiftcoder wrote: post #14
lordgrenville wrote: post #8

"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...

This is more a test of reading comprehension than algebra. Figuring out what the questions is even trying to ask is like 90% of the question.

Re: How old is Ann?

#23

Post by quuxplusone »

lordgrenville wrote: post #8

"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.

Not the Flynn effect; just people having fun, and selection bias. I (the blogger) deliberately left out many boring responses, except for linking to the Evening World's letters page of 1903-11-11.[1] I filtered out scores of replies from schoolchildren walking through the algebra to get the correct answer, and dozens of (usually short) replies from people of various ages giving wrong answers with and without reasoning, some almost certainly joking, some almost certainly not. But that's what you should expect from a Letters to the Editor section on any given math meme! Our discourse hasn't changed that much over 120 years. See my other post,[2] linked at the bottom of the current one, on "What is 8÷2(2+2)?" — that's not as fair a question, but the discourse is pretty much the same in unfiltered Letters-to-the-Editor sections: "I think it's X. Well, I think it's Y."

The whole point of this kind of meme is for the populace to perform disagreement about the answer! (See also: the Monty Hall problem; sports; comments sections.)

[1] - https://www.loc.gov/resource/sn83030193/1903-11-11/ed-1/?sp=...

[2] - https://quuxplusone.github.io/blog/2019/08/01/what-is-8-divi...

Re: How old is Ann?

#24

Post by [deleted] »

judofyr wrote: post #9

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.

[deleted]

Re: How old is Ann?

#25

Post by pmontra »

tempfile wrote: post #13

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.

It's a kind of cheating because it means not understanding the essence of the problem but with such small numbers enumeration is a viable strategy.

> Mary is 24 years old. She is twice as old as Ann was

So Ann was 12

> when Mary was as old as Ann is now

So Mary is older than Ann.

The age of Ann is somewhere between 12 and 24. Without much thinking I'd say that probably 12 and 24 are not included and probably it is an even number.

We can test each of them.

If Ann is 14 now, when Mary was 14 (10 years ago) Ann was 4 year old and Mary would be 8 now, this is not the solution.

If Ann is 16 now, when Mary was 16 (8 years ago) Ann was 8, Mary would be 16 now, nope.

If Ann is 18 now, when Mary was 18 (6 years ago) Ann was 12, Mary would be 24 now and she is. This is the solution.

Ann is 18.

Re: How old is Ann?

#26

Post by skipants »

Here's the simplest form I could distill it to. The other comments I find quite verbose or confusing, no offense intended.

    x: Ann's current age
    y: The age difference between Ann and Mary

    24 = x + y      (ie. their current ages)
    x = (24/2) + y  (ie. their age in the past)

    Solve for y in one equation and plug it into the other. You'll get x = 18.

Re: How old is Ann?

#27

Post by gnodar »

judofyr wrote: post #9

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.

Ah, that makes sense. I originally read it differently.

> Mary is 24 years old. She is twice as old as Ann was when Mary was as old as Ann is now. How old is Ann?

Which I read as:

> Mary is 24 years old. When Mary was Ann's current age, Anne was half the age she currently is.

Which would mean Anne is 16 (because when Mary was 24-8=16, Anne's current age, then Anne was 16/2=8, half Anne's current age).

But re-reading it, then for that to be true the original would have needed to be phrased:

> Mary is 24 years old. She was twice as old as Ann was when Mary was as old as Ann is now. How old is Ann?

Re: How old is Ann?

#28

Post by zephen »

skipants wrote: post #21
zephen wrote: post #17

Earlier quoted context omitted.

> 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…

Uhhh... what? The OP is right; even if you do it intuitively it's still algebra. If you need a proverb to justify it: Just because your hammer is made of stone doesn't make it less of a hammer.

Thanks for the downvote.

Look, when someone says "you need algebra to solve this" is it reasonable to assume that they are talking about informal methods that people have used forever, or is it more reasonable to assume they are talking about formal algebraic methods?

Because many people sure as shit don't need any algebraic symbols or operators to solve this in their heads.

Re: How old is Ann?

#29

Post by brazzy »

lukewarm707 wrote: post #11
Cockbrand wrote: post #7

Earlier quoted context omitted.

Sounds about right. How I understand it: Mary is 24, Ann is a few (n) years younger M = 24 A = M-n Mary is twice as old as Ann was when Mary was as old as Ann is now. So we have to deduct the age difference twice from Mary's current age to find out how old Ann was when Mary was as old as Ann is now, which is half Mary's current age: M-2n = M/2 = 12 M-2n = 12 --> n=6 So the age difference is 6, and Ann is 18.

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

For me they key step to solving it was realizing that

mary_curr - mary_old = ann_curr - ann_old

since they must have aged the same amount of years.

time dilation joke incoming

Re: How old is Ann?

#30

Post by quuxplusone »

feelamee wrote: post #6

what the true answer? oh, there is no? My intuition says that Ann now is 24

> Dozens of people declare solemnly that Mary and Ann are twins, though the slightest attempt to "prove" this shows it does not fulfil the conditions of the problem. [...] "About Mary and Ann, I think they are eight years old," says a woman, disregarding the first words of the question, which state that Mary is twenty-four.

[1] - https://www.loc.gov/resource/sn88085488/1903-10-31/ed-1/?sp=...

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