Math problem

[Night Elf]

DH thought someone here might be interested in this article that gives a math problem from Singapore. Apparently, it's been all over facebook. The article gives a hint, but doesn't give the answer. I don't do logic puzzles so I didn't even attempt this :)

[Mergath]

I had to look up the answer. Once you read the answer it makes sense, but when I first saw it I had no clue.

[5of5]

I saw this earlier today.  I figured it out easily enough, but I did have an advantage in that I have a somewhat similar type of problem in the form of a cartoon about beer drinking.

 

ETA: Needless to say, beer drinking problems are inherently more interesting. :laugh:

[mom2bee]

July 16? I think...:unsure: Where are all the mathy people when you need them?

[5of5]

Yes, July 16.

[Suzanne in ABQ]

Yup.  Keyword in first clue is "know".

[Liz CA]

I cannot get past the grammar mistake. Should it not read "either?" And then the tense is wrong in the other sentence. :)

[go_go_gadget]

I live in a house in which children watching Labyrinth for the first time stand up and shriek ''Smullyan!'' during the appropriate scene, so this is second nature to me.

[maize]

I cannot get past the grammar mistake. Should it not read "either?" And then the tense is wrong in the other sentence. :)

 

Too instead of either could be local usage, evolving language and all...

 

I enjoyed the problem.

[plansrme]

I got it as well.  The key (for me) is the going back-and-forth.  Is there a prize?  I'm pretty sure I deserve a prize for being smarter than some Singaporean fifth grader.

 

P.s.  That was cool.  Thanks for posting!

[Arcadia]

This math problem has been floating on my Facebook thread with the link to The Guardian online. I think my country's test writers has never vetted maths exams questions for grammar. It is for the Singapore Math Olympiad anyway and not a routine classroom math question.

 

July 16? I think...:unsure: Where are all the mathy people when you need them?

Spoiler alert. Solution/explanation in link

http://mothership.sg/2015/04/p5-logic-question-is-actually-a-math-olympiad-question-for-sec-3-and-4-students/

[Night Elf]

I got it as well.  The key (for me) is the going back-and-forth.  Is there a prize?  I'm pretty sure I deserve a prize for being smarter than some Singaporean fifth grader.

 

P.s.  That was cool.  Thanks for posting!

 

I'd offer a cupcake, but that could turn this thread into a controversial one. :)

[Tsuga]

I wasted a good minute or two on that at work. Sadly was interrupted with a work-related phone call and was not able to time myself. I love this sort of problem and have done hundreds in my life... for fun...

[Spy Car]

Glad I've been doing Singapore math with the rug-rat all these years :)

 

Bill

[creekland]

Ok... I thought that was an easy logic question compared to some I've seen, but then again, I spent a bit of my time two weeks ago trying to convince some 9th graders that 28x7 = 7x28, so it doesn't surprise me that many would be stumped - esp since there are words involved and a calculator won't help them.

[Seasider]

I cannot get past the grammar mistake. Should it not read "either?" And then the tense is wrong in the other sentence. :)

Seriously! It isn't a math problem, it's a grammar problem!

[Southern Ivy]

This made me realize how horrid I am with logic. 
Does anyone have any links to free logic practice? 

[momto10blessings]

Am I the only one still confused after reading the solution? Bad day to quit drinking coffee.

[5of5]

What part of it don't you follow?

[SamanthaCarter]

This was humiliating. :/ 

[creekland]

This was humiliating. :/ 

 

Eh, it's a logic problem.  Some folks are naturally good at them and others aren't.  It's really no big deal either way and says nothing about the worth of the person.

 

It's a good thing artistic ability is that way too.  I'm horrid at drawing or painting anything.  Hubby helped my boys with all their projects in their lives.  I could help them with the more concrete thinking things - like logic problems.

 

Now, if you can't answer 28x7 = 7x___ without a calculator like the majority of 9th graders in my class a couple of weeks ago, THEN we have a logic (and math) problem.  Even when I broke down and let some use the calculator about half didn't believe the answer could be correct since it's in the first part of the problem (sigh).

 

Problems like these?  It's ok if one doesn't "see" it IMO.  Some of us just are good at them and like them in the same way that some like doodling or writing poetry.

[wendyroo]

Am I the only one still confused after reading the solution? Bad day to quit drinking coffee.

 

Let's just take it one statement at a time and cross out the impossible options.

 

The options:

May 15, May 16, May 19

June 17, June 18

July 14, July 16

August 14, August 15, August 17

 

We know that Albert knows the month: either May, June, July or August.

We know that Bernard knows the date: either 14, 15, 16, 17, 18 or 19.

 

Albert says: "I don't know when Cheryl's birthday is,"

Obviously, no matter what month he was told there would always be multiple possibilities.

 

Then Albert says: "but I know that Bernard does not know too."

How would Bernard know since all he knows is the date?  Well, if the date was 19 then it would have to be May 19 and if the date was 18 then it would have to be June 18.  How does Albert know that Bernard does not know?  He has to know that the birthday could not be May 19 or June 18.  He must have been told that the birthday falls in July or August.

 

Remaining options:

May 15, May 16, May 19

June 17, June 18

July 14, July 16

August 14, August 15, August 17

 

Bernard says: "At first I do not know when Cheryl's birthday is, but I do know now."

By the same logic we used, Bernard now knows that the birthday is in July or August.  If he had been told the date was the 14th, then he still would not know if it was July 14 or August 14.  He must have been told 15, 16, or 17.

 

Remaining options:

May 15, May 16, May 19

June 17, June 18

July 14, July 16

August 14, August 15, August 17

 

Lastly, Albert says: "Then I also know when Cheryl's birthday is."

If he had been told the birthday was in August, then he still would not know if it was August 15 or August 17.  Since he does now know the birthday, then he must have been told it was in July which means it must be July 16th.

 

Wendy

[maize]

Nicely explained, Wendy.

[momto10blessings]

Let's just take it one statement at a time and cross out the impossible options.

 

The options:

May 15, May 16, May 19

June 17, June 18

July 14, July 16

August 14, August 15, August 17

 

We know that Albert knows the month: either May, June, July or August.

We know that Bernard knows the date: either 14, 15, 16, 17, 18 or 19.

 

Albert says: "I don't know when Cheryl's birthday is,"

Obviously, no matter what month he was told there would always be multiple possibilities.

 

Then Albert says: "but I know that Bernard does not know too."

How would Bernard know since all he knows is the date? Well, if the date was 19 then it would have to be May 19 and if the date was 18 then it would have to be June 18. How does Albert know that Bernard does not know? He has to know that the birthday could not be May 19 or June 18. He must have been told that the birthday falls in July or August.

 

Remaining options:

May 15, May 16, May 19

June 17, June 18

July 14, July 16

August 14, August 15, August 17

 

Bernard says: "At first I do not know when Cheryl's birthday is, but I do know now."

By the same logic we used, Bernard now knows that the birthday is in July or August. If he had been told the date was the 14th, then he still would not know if it was July 14 or August 14. He must have been told 15, 16, or 17.

 

Remaining options:

May 15, May 16, May 19

June 17, June 18

July 14, July 16

August 14, August 15, August 17

 

Lastly, Albert says: "Then I also know when Cheryl's birthday is."

If he had been told the birthday was in August, then he still would not know if it was August 15 or August 17. Since he does now know the birthday, then he must have been told it was in July which means it must be July 16th.

 

Wendy

I'm embarrassed. My brain really wasn't working this morning.

I read that there was 3 boys. Which didn't make any sense. Seriously, I thought the boys were Albert, Bernard and Charlie. I HAVE NO CLUE how my brain did that. Maybe coffee is good for me?

Thanks for the explanation though.

[Okra]

That was fun!  I have children that will like this.

 

By the way, Im not mathy, I was not able to solve this, but my children will still think it is fun.

[DragonFaerie]

Let's just take it one statement at a time and cross out the impossible options.

 

The options:

May 15, May 16, May 19

June 17, June 18

July 14, July 16

August 14, August 15, August 17

 

We know that Albert knows the month: either May, June, July or August.

We know that Bernard knows the date: either 14, 15, 16, 17, 18 or 19.

 

Albert says: "I don't know when Cheryl's birthday is,"

Obviously, no matter what month he was told there would always be multiple possibilities.

 

Then Albert says: "but I know that Bernard does not know too."

How would Bernard know since all he knows is the date?  Well, if the date was 19 then it would have to be May 19 and if the date was 18 then it would have to be June 18.  How does Albert know that Bernard does not know?  He has to know that the birthday could not be May 19 or June 18.  He must have been told that the birthday falls in July or August.

 

Remaining options:

May 15, May 16, May 19

June 17, June 18

July 14, July 16

August 14, August 15, August 17

 

Bernard says: "At first I do not know when Cheryl's birthday is, but I do know now."

By the same logic we used, Bernard now knows that the birthday is in July or August.  If he had been told the date was the 14th, then he still would not know if it was July 14 or August 14.  He must have been told 15, 16, or 17.

 

Remaining options:

May 15, May 16, May 19

June 17, June 18

July 14, July 16

August 14, August 15, August 17

 

Lastly, Albert says: "Then I also know when Cheryl's birthday is."

If he had been told the birthday was in August, then he still would not know if it was August 15 or August 17.  Since he does now know the birthday, then he must have been told it was in July which means it must be July 16th.

 

Wendy

 

Thank you for the explanation.  I'm still an idiot.   :willy_nilly:

[Guest]

I had to look up the answer. Once you read the answer it makes sense, but when I first saw it I had no clue.

Yes, I'm getting pretty good at logic puzzles now that I am teaching them to my children, but this one was beyond me. I never had much exposure to them except for one excellent math teacher who felt they were important. And now that I know what I do, I'm hoping my children will see a problem like this and be excited to tackle it, not totally lost like mama!

[Guest]

Let's just take it one statement at a time and cross out the impossible options.

 

The options:

May 15, May 16, May 19

June 17, June 18

July 14, July 16

August 14, August 15, August 17

 

We know that Albert knows the month: either May, June, July or August.

We know that Bernard knows the date: either 14, 15, 16, 17, 18 or 19.

 

Albert says: "I don't know when Cheryl's birthday is,"

Obviously, no matter what month he was told there would always be multiple possibilities.

 

Then Albert says: "but I know that Bernard does not know too."

How would Bernard know since all he knows is the date? Well, if the date was 19 then it would have to be May 19 and if the date was 18 then it would have to be June 18. How does Albert know that Bernard does not know? He has to know that the birthday could not be May 19 or June 18. He must have been told that the birthday falls in July or August.

 

Remaining options:

May 15, May 16, May 19

June 17, June 18

July 14, July 16

August 14, August 15, August 17

 

Bernard says: "At first I do not know when Cheryl's birthday is, but I do know now."

By the same logic we used, Bernard now knows that the birthday is in July or August. If he had been told the date was the 14th, then he still would not know if it was July 14 or August 14. He must have been told 15, 16, or 17.

 

Remaining options:

May 15, May 16, May 19

June 17, June 18

July 14, July 16

August 14, August 15, August 17

 

Lastly, Albert says: "Then I also know when Cheryl's birthday is."

If he had been told the birthday was in August, then he still would not know if it was August 15 or August 17. Since he does now know the birthday, then he must have been told it was in July which means it must be July 16th.

 

Wendy

You're awesome. Please feel free to walk around today feeling just slightly superior for your logic mojo ;)

[kiana]

http://www.newyorker.com/cartoons/daily-cartoon/daily-cartoon-thursday-april-16th-cheryl-singapore-math?mbid=social_facebook

 

(related)

[Guest]

http://www.newyorker.com/cartoons/daily-cartoon/daily-cartoon-thursday-april-16th-cheryl-singapore-math?mbid=social_facebook

 

(related)

HA! Indeed.

[creekland]

http://www.newyorker.com/cartoons/daily-cartoon/daily-cartoon-thursday-april-16th-cheryl-singapore-math?mbid=social_facebook

 

(related)

 

I wonder that about many logic problems.  There are plenty of twisted minds in math.  I suppose it's kind of like a private club or something.  ;)

[Seasider]

I wonder that about many logic problems. There are plenty of twisted minds in math. I suppose it's kind of like a private club or something. ;)

I don't think it's constrained to just math folk. The first logic puzzle of this sort was thrown at me by a law student, whose was regularly challenged by one of his profs.

[5of5]

When I first read the puzzle, it reminded me something I worked on as a kid but goes around the internet from time to time:

 

http://en.wikipedia.org/wiki/Zebra_Puzzle

 

Be warned!  This one is a bit more difficult than this birth date problem.

[Bluegoat]

Yes, I'm getting pretty good at logic puzzles now that I am teaching them to my children, but this one was beyond me. I never had much exposure to them except for one excellent math teacher who felt they were important. And now that I know what I do, I'm hoping my children will see a problem like this and be excited to tackle it, not totally lost like mama!

 

We did a unit on logic puzzles when I was in school, but not at all connected to math.  Calling it a math question kind of threw me off, i don't really think of it that way at all.

[Arcadia]

I don't think it's constrained to just math folk. The first logic puzzle of this sort was thrown at me by a law student, whose was regularly challenged by one of his profs.

LSAT :lol:

I have used library's LSAT prep books for my kids entertainment because I am too cheapskate to buy logic puzzle books.

[go_go_gadget]

When I first read the puzzle, it reminded me something I worked on as a kid but goes around the internet from time to time:

 

http://en.wikipedia.org/wiki/Zebra_Puzzle

 

Be warned!  This one is a bit more difficult than this birth date problem.

 

That was fun, thanks!

[Leav97]

I'm still a little lost.

 

Let's just take it one statement at a time and cross out the impossible options.

 

The options:

May 15, May 16, May 19

June 17, June 18

July 14, July 16

August 14, August 15, August 17

 

We know that Albert knows the month: either May, June, July or August.

We know that Bernard knows the date: either 14, 15, 16, 17, 18 or 19.

 

Albert says: "I don't know when Cheryl's birthday is,"

Obviously, no matter what month he was told there would always be multiple possibilities.

 

Then Albert says: "but I know that Bernard does not know too."

How would Bernard know since all he knows is the date?  Well, if the date was 19 then it would have to be May 19 and if the date was 18 then it would have to be June 18.  How does Albert know that Bernard does not know?  He has to know that the birthday could not be May 19 or June 18.  He must have been told that the birthday falls in July or August.

 

Remaining options:
May 15, May 16, May 19
June 17, June 18
July 14, July 16
August 14, August 15, August 17

 

Bernard says: "At first I do not know when Cheryl's birthday is, but I do know now."

By the same logic we used, Bernard now knows that the birthday is in July or August.  If he had been told the date was the 14th, then he still would not know if it was July 14 or August 14.  He must have been told 15, 16, or 17.

 

All of this makes sense to me.

 

Remaining options:
May 15, May 16, May 19
June 17, June 18
July 14, July 16
August 14, August 15, August 17

 

Lastly, Albert says: "Then I also know when Cheryl's birthday is."  I don't see how Albert could know.  Bernard can figure it out because he knows the # and it has to be unique.  That only narrows down the list to the last 3.  How would Albert know?  I get how we know it's July 16th because we take Albert's comment at face value.  I just don't get how Albert knows.

 

If he had been told the birthday was in August, then he still would not know if it was August 15 or August 17.  Since he does now know the birthday, then he must have been told it was in July which means it must be July 16th.

 

Wendy

 

Oh Duh, I get it know.  Albert knows the month.  Therefore, he has narrowed it down to 1 possible.  Nevermind.  I get it now.

[Tsuga]

When I first read the puzzle, it reminded me something I worked on as a kid but goes around the internet from time to time:

 

http://en.wikipedia.org/wiki/Zebra_Puzzle

 

Be warned!  This one is a bit more difficult than this birth date problem.

 

This is like those found in logic puzzle books. I loved these as a child.

[Liz CA]

When I first read the puzzle, it reminded me something I worked on as a kid but goes around the internet from time to time:

 

http://en.wikipedia.org/wiki/Zebra_Puzzle

 

Be warned!  This one is a bit more difficult than this birth date problem.

 

I do love these. You make a grid and fill it in. There is a whole series of books I used to do with ds for logic.

[CaffeineDiary]

If you liked this sort of puzzle, you want to try Everett Kaser's games Sherlock, Honeycomb Hotel, Dinner with Moriarty, and others, available from http://kaser.com.  They're basically a gamification of this sort of question :-)
 

[momto10blessings]

I do love these. You make a grid and fill it in. There is a whole series of books I used to do with ds for logic.

Do you know what the series was? Apparently I need some practice ;)

[Miss Tick]

Logic Safari is one of those series. It's too young for you, though, unless you have an elementary kid you can give it too to finish the ones you don't need! Sudoku or Ken-Ken have the same logical approach, but with numbers instead of words.

[Arcadia]

Do you know what the series was? Apparently I need some practice ;)

 

I don't know what the series is but you can get free samples of the logic grid kind here.   

 

You would need to click on Sample Puzzles, and then click on Logic & Math

https://www.pennydellpuzzles.com/free_puzzles/default.aspx

 

Also here http://www.printable-puzzles.com/printable-logic-puzzles.php