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Pratakosong

Difficult PSLE 2019 Math Question!

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Twincharged
On 9/30/2019 at 10:57 AM, Ender said:

O level too chim for me. Unable to relearn the A math. My son is on his own there, only can support for math tuition outside.

You find O level Math too chim for you ah? I worse hor I findupper primary Math too chim. 不不不

A Math is usually quite difficult. There's a very good Secondary Math teacher in Mavis Compass One. He taught my girl.

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2nd Gear (edited)
38 minutes ago, Hiphiphoray said:

Can I ask the maths expert here on the egg tart question.

My son got the answers as 46 tarts and $1.53, same as me...色.but the outside world says the answer is 40 tarts and $1.80.

I cannot let go of this...色..cant eat cant sleep......but my son already lost in the Plug-G world liao...........lol.

Got the screenshot from a facebook post that's been going around.

I think it would be easier to think of it as Jamie got a 15% discount and hence only need to pay $61.20 (after he has gotten the 15% discount)

So since 85% is $61.20, we just need to calculate how much did Jamie would have paid if he did not enjoy the 15% discount which is $61.20 / 85 X 100 = $72

Hence, Jamie paid full price $72 and X paid full price $61.20

And since Jamie bought 6 more egg tarts than X, that means Full price of each egg tart = ($72-$61.20) / 6 = $1.80

71185963_10157495982634477_5369928547114680320_n.jpg

Edited by Pratakosong
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Twincharged
7 minutes ago, Turboflat4 said:

Don't disagree with most of what you say but why denigrate those students who go to N(T)?

I didn't denigrate. I just dun want my son to takethe longer route. But most important he must be happy and healthy. 撘敹撠勗末

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Supersonic
9 minutes ago, Dleodleo said:

Aiyo! I dun understand why these parents make a big huha about the Math paper. It's already over and why can't they just relax? There's sure few difficult questions in national exam. These parents must be the kiasu one who scare these questions will affect their chances of getting A*.

My son is P6 this year and he's weak in Math. I dun even bother about these difficult questions. Dun knw just skip or anyhow do lor.

To me as long as he pass his PSLE and promote to secondary school and dun go normal techcan liao.

PSLE is already over! It's party time!

After seeing the 3 questions, Two of them is within the PSLE syllabus. i.e. if they have done their homework,and extra consistent hard work to practiceshould be able to tackle.

The triangle, especially part C, that is difficult. I couldnt get that one too.. hahahaha..

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2nd Gear
14 minutes ago, Dleodleo said:

Aiyo! I dun understand why these parents make a big huha about the Math paper. It's already over and why can't they just relax? There's sure few difficult questions in national exam. These parents must be the kiasu one who scare these questions will affect their chances of getting A*.

My son is P6 this year and he's weak in Math. I dun even bother about these difficult questions. Dun knw just skip or anyhow do lor.

To me as long as he pass his PSLE and promote to secondary school and dun go normal techcan liao.

PSLE is already over! It's party time!

Party Time? GE coming liao ah? ... Oh wrong thread ...

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Supersonic
6 minutes ago, Dleodleo said:

You find O level Math too chim for you ah? I worse hor I findupper primary Math too chim. 不不不

A Math is usually quite difficult. There's a very good Secondary Math teacher in Mavis Compass One. He taught my girl.

Thanks for the kai siao.. Next time my girl go secondary school, will check out mavis at compass one..

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2nd Gear
1 minute ago, Ender said:

After seeing the 3 questions, Two of them is within the PSLE syllabus. i.e. if they have done their homework,and extra consistent hard work to practiceshould be able to tackle.

The triangle, especially part C, that is difficult. I couldnt get that one too.. hahahaha..

I think this slides explain part c of the triangles question quite well ... took a while to get it too. Best to approach such pattern questions with a fresh mind.

71065877_2936686313025380_8402097568858767360_o.png

71388012_2936686316358713_1976305200977149952_o.png

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6th Gear
42 minutes ago, Turboflat4 said:

Unfortunately you and your son have a major misunderstanding of percentage discounts.

When something is discounted (decreased) by 15 percent, its price becomes 85 percent of what it was originally.

What you're given is the discounted price. To calculate the original, you should take 61.20 x 100/85 to find the undiscounted price of Jamie's donuts.

What you and your son very likely did is 61.20 x 115/100, which would only make sense if they told you the original price was 61.20, and they asked you to calculate the price after a 15 percent mark-up (increase).

A lot of smart people trip over this basic thing which is actually very important in everyday commerce. The author of Dilbert, Scott Adams, a MENSA member, was also caught out when he made a strip with this error (albeit in a more subtle fashion).

Just in case you can't see what I'm talking about:

The correct way:

Jamie's undiscounted price would've been 61.20 x 100/85 = 72, which is 72 - 61.20 = 10.80 more than the other guy paid. So 6 donuts is 10.80, and one donut is 1.80, so the other guy bought 61.20/1.80 = 34 donuts and Jamie bought 34+6=40.

Your (erroneous) way:

Jamie's undiscounted price would've been 61.20 x 115/100 = 70.38, which is 70.38 - 61.20 = 9.18 more than the other guy paid. So 6 donuts is 9.18 and one donut is 1.53, so the other guy bought 61.20/1.53 = 40 donuts and Jamie bought 40+6=46.

You'd probably have figured out something was wrong if you'd gotten ugly answers, but the trend now is to set questions that return reasonably nice answers if you make a common error just to mess with you haha .

100% = 61.20. Not 70.38

Hence 9.18/61.20 x 100 = 15%......no ?

Confuse Confuse Confuse...色...lolllllll

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Supersonic (edited)
1 minute ago, Hiphiphoray said:

100% = 61.20.

85% is 61.20 for Jamie.

Edited by Turboflat4
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Supersonic (edited)
22 minutes ago, Ender said:

After seeing the 3 questions, Two of them is within the PSLE syllabus. i.e. if they have done their homework,and extra consistent hard work to practiceshould be able to tackle.

The triangle, especially part C, that is difficult. I couldnt get that one too.. hahahaha..

The triangle one is easy if you understand number sequences (it's a staggered "triangular number" sequence and is related to the sum of the first n positive integers) but that's well beyond normal PSLE of course.

I tend to find things like the triangle thing much, much easier than the semicircles. Pure numerical and symbolic reasoning comes much easier to me than spatial stuff.

Edited by Turboflat4

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6th Gear (edited)
45 minutes ago, Pratakosong said:

I think this slides explain part c of the triangles question quite well ... took a while to get it too. Best to approach such pattern questions with a fresh mind.

71065877_2936686313025380_8402097568858767360_o.png

71388012_2936686316358713_1976305200977149952_o.png

The 1 x 1, 2 x 2 , 3 x 3 is pretty standard stuff.

The rest is all about patterns and difference.

Odd & Even is considered pattern...色.so its within the PSLE realm.

Not a difficult question. Manageable with a clear mind.

The problem is....setting it at the very last question, most pupils' brain already in moderate to high Haze levels liao色色.lol

I guess the Maths T-score will be push up 5 points at least ???

Edited by Hiphiphoray

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Supersonic
48 minutes ago, Pratakosong said:

I think this slides explain part c of the triangles question quite well ... took a while to get it too. Best to approach such pattern questions with a fresh mind.

71065877_2936686313025380_8402097568858767360_o.png

71388012_2936686316358713_1976305200977149952_o.png

I didn't see that pattern of the incremental difference. That's why stucked at part C

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Neutral Newbie (edited)
On 9/28/2019 at 7:33 AM, Pratakosong said:

The answer to this is assuming it is symmetrical which is true since the lengths on the left mirrors the right.

The diameter of the second semicircle (from the left)is:

(D-22)+12+(D-16)/2 = D
D=36

Tbh I think it's too hard for kids.

Edited by coverpage

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Neutral Newbie (edited)
On 9/28/2019 at 7:42 PM, Pratakosong said:

This is really too difficult for kids.

250^2 is the total just from looking at how the n sequence is related to the total through the function, the total = n^2

To find the percentage first let k be the number of white triangles

k+k+250 = 250^2 (because the difference between the grey and white triangle is 250)

k = (250^2-250)/2 = 31125

(k+250) is the number of grey triangle

Percentage of grey triangleis therefore(k+250)/250^2 = 0.502 or 50.2%

I don't really like this question as I'm not sure if it teaches kids how to apply mathematics but rather to test on their ability for pattern recognition in exam condition with a limited amount of time. I'm not sure if it's representative of their mathematical capability or potential.

Edited by coverpage

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Neutral Newbie

Hey Friends - I think, students should always keep an option to attempt such problem using simple algebra. Although modelling approach is very strongly advocated in all Primary schools, some of the problems are much easier to solve using simple algebra. Using simple algebra studentsbe able to solve this problem in threelines.

Assume diameter of the circle is "d".

From the top of the picture : total lenght of the line = d+12+d+12+d = 3d +24

From the bottom of the picture : total lenght of the line = 22+d+16+d+22=2d+60

=> 3d+24 = 2d+60

=> 3d-2d = 60-24

=> d = 36

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5th Gear
10 hours ago, Hiphiphoray said:

Can I ask the maths expert here on the egg tart question.

My son got the answers as 46 tarts and $1.53, same as me...色.but the outside world says the answer is 40 tarts and $1.80.

I cannot let go of this...色..cant eat cant sleep......but my son already lost in the Plug-G world liao...........lol.

All's not lost. Your son's answer is almost there, except that 1.53 is the discounted unit price.

The regular unit price is 1.53/0.85 = 1.80.

He should get partial marks for this qn.

Sometimes an irregular answer is reason to recheck e.g. at primary school level, cost of simple goods is unlikely to be an odd number like 1.53. Assuming the question setter is conscientious.

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2nd Gear
1 hour ago, deycom1 said:

Hey Friends - I think, students should always keep an option to attempt such problem using simple algebra. Although modelling approach is very strongly advocated in all Primary schools, some of the problems are much easier to solve using simple algebra. Using simple algebra studentsbe able to solve this problem in threelines.

Assume diameter of the circle is "d".

From the top of the picture : total lenght of the line = d+12+d+12+d = 3d +24

From the bottom of the picture : total lenght of the line = 22+d+16+d+22=2d+60

=> 3d+24 = 2d+60

=> 3d-2d = 60-24

=> d = 36

At the P6 standard, the students do have a chapter covering Algebra. But modelling is would still be very easy for this question if you convert all the semicircles into rectangular boxes.

screenshot.PNG

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