Monday, October 20, 2008

Singapore Math 3

Found these two PSLE 2008 questions from a parenting forum.

Question 1:

In April, 40% of the people who went to the museum were children. The rest were adults. The number of women was 3/4 the total number of adults. The rest were men.

In May, the number of children increased by 20%. The number of adults was the same as in April but the number of women became only 3/5 of the adults. Then, the number of children became 336 more than the number of women.

a) What is the ratio for the number of children to the number of men to the number of women in April?
b) How many people went to the museum in May?

Brian's solution: Using ratios
a) is straightforward; C:M:W --> 40:15:45 --> 8:3:9

b)
Before
C:W:M --> 8:9:3

After
20% increase in children --> 8X1.2 = 9.6
W:M --> 3:2 (total 5 units)
convert from earlier W:M ratio of 9:3 (12 units); so multiply by 12 and divide by 5
W:M --> 7.2:4.8 (12 units)

Therefore
C:W:M --> 9.6:7.2:4.8
--> 96: 72: 48
--> 4:3:2

1 unit is therefore 336.
9 units will be 336 x 9 = 3024.

3024 people went to the museum in May.

Is there a model method for the above question? Brian couldn't do it using models.

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Question 2

Brian invited some boys and girls, there are 20 more boys than girls. 3/4 of the boys and 2/3 of the girls managed to come. 19 children did not come. How many children did Brian invite?

Solutions may be sent to mathsingapore at gmail dot com. Thanks!

I confess I could do neither question above (the second one I was okay with algebra, not model), so stop calling me a Math whiz mum. Can't even solve PSLE questions!

****************************

For model solution: Check out Monica's post.

Anonymous said...

(unprintable expletive)!!!!????!!!!

YY.

Lilian said...

YY, the general feedback is this year's PSLE Math is easy!

*faint* lor....

monlim said...

Can I post the answers in my blog? I don't know how to post it in comments...

Lilian said...

Yes, yes, please do, thanks!

monlim said...

Sorry, got to rush out urgent job so will post later. btw, Brian got all the answers correct, so he's well prepared for PSLE. They don't care what method you use as long as it's logical and gives the answer. One boy in L-A's class loves to use algebra and the teacher says it's accepted.

Lilian said...

No prob, take your time. Thanks!

Anonymous said...

monlim: "One boy in L-A's class loves to use algebra and the teacher says it's accepted."

Maybe coz it's GEP & they're more 'enlightened'. Suay suay kena ngiao teacher in non-GEP class how? Was L-A's teacher speaking for the PSLE marking scheme?

What if the question specifies 'must use model method', how?

YY.

Anonymous said...

btw hor, how can it be PSLE 2008 questions? You mean the PSLE this year finished oredi huh?

YY.

Lilian said...

YY, I think algebra is allowed in PSLE. See this.

Trouble is sometimes it's really hard to do it with algebra, many variables involved, so you'll waste time solving it this way. Easier and faster with model for those who are adept at using it.

Anonymous said...

Goodness you mean they've taught algebra at P6 already huh?

And btw, how come Brian so smart one?? Whose genes izzit? Oh I know, must be Malaysian genes. Maybe I should show these questions to my brother in UK and 'scare' him a bit... He'd better not think of going back to Sgp liao.. haha!

YY.

monlim said...

YY: No, this is not specific to GEP, it's accepted by all. The questions don't say that you have to use any particular method.

That's why some homeschoolers choose not to use model method, as long as they know how to solve the problem.

Lilian said...

Ay YY, you went through PSLE questions with your girl what, so should not be an eye-opener for you. For us, it's a shock to the system lah.

Aiyoh, there are tonnes more kids in Sg smarter than him lah, tonnes. That's why very scared to go back too! haha...

Lilian said...

Yes, YY, PSLE over liao...wake up :)

Mon: I think the model method is really superior in that kids build solid foundation in concepts with true understanding of basic math. Just wondering, do the kids continue to use these in secondary school?

monlim said...

Don't know if this comment went thru but I was saying you need to bear my 3 assumptions in mind, esp the one where each unknown part of the model has to be of equal value. Otherwise it won't work, which is where I think you and Brian stumble. Just takes practice, I'm sure you'll master it in a while.

YY: The kids are not taught algebra at p6. The ones who use it are the smart alecky ones who learn algebra on their own :)

See, I shd be working, yet keep taking peeks here!!

Anonymous said...

My girl's PSLE was in 2002 mah, like a lifetime ago..

I vaguely remember I sometimes had to look at the answers first and learn how to do that 'type' of questions & from then on questions of a similar 'type' became easy.

It was a matter of trying out as many types of 'models' as possible from as many sources as possible. After a while I began to notice that I could answer most of the questions, having tried similar 'type' models before. But I realize in PSLE, there would be 1 or 2 questions that would be totally 'out of the blue'. Those are the questions that the kids 'cry' over!!

Hey, if I'd never tried those questions before, I really think I would have pee'd in my underwear before I could answer them in the PSLE...

So the PSLE presupposes that the kids would have been coached on & would have tried out similar 'type' questions already & doesn't really expect kids to know how to figure out these things 'fresh'. That's why a foreigner looking at these questions would think we're trying to train up 'geniuses'. But they will think up 1 or 2 'novel' questions to sieve out the real geniuses. My friend whose daughter spent a few years in UK and then a few years in USA was able to answer one of such questions while her cohort couldn't. My friend attributed it to the creativity her daughter was exposed to abroad. Of course my friend also ordered 'Andrew Er' stuff to let her daughter practise, lah!

I don't know if you remember, maybe round about 2000 there was a question that asked the kids to add 1+2+3.... all the way to 100.

Apparently some of the kids had tried that question or similar questions before so they could answer. Those who hadn't tried before, couldn't.

YY.

Lilian said...

Yup Mon, your comment was on the other post. Do keep those assumptions in mind, but just don't see it lah sometimes. I think the basic foundation for doing models deftly is just not there.

YY: Yup, I remember the big ruckus over that 1+2+3....99+100 question, haha, now every kid knows how to do it. So every year the folks at MOE have to think up ever more convulated questions, also gotta pity them lah! But pity us more!

Anonymous said...

model mom...basic algebra is taught at P6.

And you can use it to solve psle maths questions, provided your working is correct.

This year, there was a boy from St Hilda's who forgot to transfer his answers for Booklet A to the OAS, and only realised it when time was up, by then it was too late. The inviligator was very strict about it. So that's 20 marks gone.

Lilian said...

er...what's OAS?

Anonymous said...

Optical Answer Sheet - where you shade your correct answer. This is for the MCQ (multiple choice questions) paper.

Btw, you can find more of this year PSLE maths questions over here:

http://prischoolmaths.blogspot.com/

If your boy can do all of them, then no need to worry anymore.

Lilian said...

Wow, thanks again Model Dad, you are really resourceful!

You know what they say right, if this year's PSLE math is easy, next year's will be a killer!

Anonymous said...

that's what they say. My son was kind of disappointed that it wasn't difficult - he was hoping it would be a killer so as to boost up his T-score.

Everybody expected Science to be difficult but it wasn't too. Funnily, it was the Listening Comprehension that has many complaining. The choices given to each question were very close and tricky. One got to really pay attention to the script.

Lilian said...

I took a peek at the PSLE website and I think I'm gonna be sick! Very difficult! And kids think this is easy? Okay, time to crack the whip!

Your boy sounds brilliant.

Anonymous said...

Can you believe that all the questions posted were culled from memories from students who chatted online and then put together by the adults? The beauty of technology...

Anonymous said...

""The inviligator was very strict about it. So that's 20 marks gone.""

Siao invigilator!!! Siao siao siao.. I'd like to think that things like this would never happen in Canada--it would be considered INHUMANE, esp. in view of the magnitude of expectations placed around the PSLE. Imagine how traumatized this boy would be--how can that invigilator sleep at night??

It's things like this that'd make people want to zao hng hng..

btw have any of you watched this youtube 'meen cheh cheh' before? Hilarious!! I guess we're pretty creative when taking digs at the gahmen..
(or go youtube & search 'face green green')

YY.

Anonymous said...

My boy did the same thing too for his prelims (thank god it was the prelims and not the psle), when he realised it 5 mins before time was up. He quickly shade the answers, and was crossing his fingers that he had shaded them all correct after the paper. Got a good scolding from me, and lesson learnt.

Seems that boys tend to have this habit, of working out the answers on the question booklet itself, and leave the transfering to the last minute.

The chief inviligator should announce about 10 minutes before time's up, to remind the students to not just check their index nos. but also to make sure to shade the OAS!

Lilian said...

Yalah, invigilator so heartless, hope can appeal. Poor kid, and youo know how hard they've worked, all culminating in this one paper.

Anonymous said...

err...your misskoh link - you typed it as .c0m (and not .com)

Anonymous said...

I worked out the 'model method' to Math 3 Qn 1!

Sent it to mathsingapore@gmail.com

Correct?

YY.

Now can sleep peacefully liao..

Lilian said...

You sent me empty emails lah, no attachments...so can't go to sleep yet :)

monlim said...

Ok, finally! All model answers posted on my blog. http://hedgehogcomms.blogspot.com/2008/10/using-models-to-solve-maths-problems_20.html

Anonymous said...

ok ok, first time send attachment with hotmail.

Now should be ok liao...

YY.

zzzzzzzzzzzzzzzzzzzzzz

Lilian said...

Thanks Monica, you have no idea how much I appreciate this. It's so helpful and you are indeed a Model Mom :)

I didn't realise how lost I was in models till I saw how you did it.

Anonymous said...

alamak, how come we so gan-cheong?

Monica I thot you're supposed to be working??

YY. :-)

Lilian said...

She only needed 30 min to do the sums, so just cut short coffee break a bit lah. No problemlah...

Yes yes, I'm very gancheong, I finally realise how bad "we" are at models.

monlim said...

Finished the sums in half an hour, finished my work in 3 hours, but took me 2 hrs just to finish the post!!!!!!! Got to re-draw model so can take photo, then because macro function in lau yah camera not good, have to crop photo, then put in blog, adjust bloody alignments that always go haywire when I post new photos... aiyoh susah lah...

monlim said...

In case u misunderstand, I enjoy posting abt maths despite the technological glitches. And am glad you're finding them useful :)

Here are 2 interesting questions, they were in the p4 CASCO Challenging Maths assessment book. See if you can solve them using models.

1. Maria sold thrice as many \$5 files as \$10 files. She also sold twice as many \$10 files as \$20 files. She collected \$160 more from selling \$5 files than from selling \$20 files.
a) How much did she collect from selling \$5 files?
b) How many files did she sell altogether?

2. Joyce is 4 years old. Her mother was 25 years older than her last year.
a) In how many years' time will Joyce's age be 2/7 of her mother's age?
b) In how many years' time will Joyce's age be 3/8 of her mother's age?

Anonymous said...

Answers sent in attachment to your email. But had to use trial-&-error method for both!

Used only a bit of 'model' for the initial part of qn 1.

YY. :-(

Lilian said...

I did No2 via model and the answer is a) 6 years and b) 11 years?

No 1, I tried via model but can't really explain it, my answer is a) \$480 and b) 144?

Will try to post my models if the above is correct, else back to the drawing board, literally.

Anonymous said...

Lil: Lucky I check with your answers, I got 2 careless mistakes in the answers I sent to Monica!!

But after checking I realize your answers are correct.

A bit pengsan today because last nite was insomniac...

How come you've flown to Sgp already & still so alert can blog so much some more?!

YY.

Lilian said...

I am an incorrible internet addict, that's why. Of course, flying with the best airline in the world also helps lah hee hee :)

But seriously, very groggy, made loads of typos in a facebook reply to one of my old friends. Almost noon now, and haven't really slept much in the past 24 hours. But aim to stay outdoors so can recover from jetlag faster.

monlim said...

Lilian, you very hiong lah! So will you be bringing along your laptop to blog in Japan??? That shd be interesting for all of us!!

YY, I don't think you emailed me the answer, maybe you emailed Lilian? Anyway no need lah, just post in comment what you got!