Q&A - PSLE Math

[YLH88]

Hi VC's mum, Dharma,


Thank you so much for the solution!!

But I'm still abit confused :

Based on VC's mum's solution :
Tricia had 75% fewer stamps than Yanling means:
Tricia : Yanling
25% : 100%
Divide by 5
5 : 20

Why do we divide by 5 ? I tried using divide by 25, which will give me 1 : 4 and can't get the answer.

Based on Dharma's solution :

L : 10u – 1p -------------------------------------- ( 1 )
YL : 16u – 4p ------------------------------------- ( 2 )
T : 4u + 5p = 10u => [ 4u x 2.5 = 10u] -------- ( 3 )

Why do you change the at 1st ratio to 10 : 16 : 4 ?

I tried using T : Y : L = 2 : 8 : 5 because I change Y : L to 8 :5 and T : Y to 1 : 4, so combining both set I get 2 : 8 : 5, and I can't get the answer

Sorry still blur ... :?

[Vanilla Cake]

YLH88:

Hi VC's mum, Dharma,

Thank you so much for the solution!!
But I'm still abit confused :

Hi YLH88,
You are always welcome!
My DD1 took PSLE 2008 and DD2 will be taking PSLE 2011, so I know how you feel about PSLE exam. BTW, is your DS taking HMT?

YLH88:

Based on VC's mum's solution :
Tricia had 75% fewer stamps than Yanling means:
Tricia : Yanling
25% : 100%
Divide by 5
5 : 20

Why do we divide by 5 ? I tried using divide by 25, which will give me 1 : 4 and can't get the answer.

Yes, you can divide by 25 and you will still get the same answer:

Tricia had 75% fewer stamps than Yanling means:
Tricia : Yanling
25% : 100%
Divide by 25
1 : 4

Yanling had 60% more stamps than Lena means:
Yanling : Lena
160% : 100%
Divide by 20
8 : 5

For Yanling, LCM of 4 and 8 is 8. So, multiply by 2 and you will get:
Tricia : Yanling
1 : 4
Multuply by 2
2 : 8

Before
Yanling: Lena : Tricia
8 : 5 : 2
Multiply by 5
40 : 25 : 10

The rest of the steps is the same.

VC's mum

[YLH88]

Vanilla Cake:

YLH88:

Hi VC's mum, Dharma,

Thank you so much for the solution!!
But I'm still abit confused :

Hi YLH88,
You are always welcome!
My DD1 took PSLE 2008 and DD2 will be taking PSLE 2011, so I know how you feel about PSLE exam. BTW, is your DS taking HMT?

YLH88:

Based on VC's mum's solution :
Tricia had 75% fewer stamps than Yanling means:
Tricia : Yanling
25% : 100%
Divide by 5
5 : 20

Why do we divide by 5 ? I tried using divide by 25, which will give me 1 : 4 and can't get the answer.

Yes, you can divide by 25 and you will still get the same answer:

Tricia had 75% fewer stamps than Yanling means:
Tricia : Yanling
25% : 100%
Divide by 25
1 : 4

Yanling had 60% more stamps than Lena means:
Yanling : Lena
160% : 100%
Divide by 20
8 : 5

For Yanling, LCM of 4 and 8 is 8. So, multiply by 2 and you will get:
Tricia : Yanling
1 : 4
Multuply by 2
2 : 8

Before
Yanling: Lena : Tricia
8 : 5 : 2
Multiply by 5
40 : 25 : 10
The rest of the steps is the same.

VC's mum

Hi VC's mum,

Nope, my DS not taking HCL, so last day will be next Monday, I can relax after that ..... phew ...

So sorry, why do we need to multiple by 5 ?

[tianzhu]

Hi YLH88


This question touches on the concept of unchanged total quantity.

The stamps are transferred internally but the total number of stamps remains the same in the beginning as well as in the end.

You may solve it using MD or Units method. I suggest using the UM for this question.

A student should be familiar with the concept of equivalent ratios so as to handle this question well.

You’ll notice that Yan Ling is repeated in comparisons with Lena and Tricia. Therefore we have to make Yan Ling’s units the same when comparing.

Once you understand the concept, the rest is just selecting comfortable equivalent units where one can work out the calculations more easily. In this particular question, 15 units is a reasonable number. Why? It can easily be divided into the ratio of 4:1 and also it very neat to increase 10 units by 15 units to 25 units.

It just leaves me to wish your kid a very successful PSLE 2010.

Best wishes

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[YLH88]

Hi VC’s mum, Dharma, TianZhu,


Thank you for the solution! Finally I understand, we changed by multiply by 5 is to suit the question for easy computation. Sigh… must be the stress and very nervous that’s why my brain not working properly…

Thank you thank you!!

[BigDevil]

http://postimage.org/image/2ryb5fmmc/

I can work out the answer to be a)90 ; b)$16.80. But could someone tell me what is the best method to use to solve this question?

[tianzhu]

Hi


Hope this helps.

Best wishes.

http://farm5.static.flickr.com/4144/5059076235_e9518fc671_b.jpg\">

[iFruit]

BigDevil:

http://postimage.org/image/2ryb5fmmc/

I can work out the answer to be a)90 ; b)$16.80. But could someone tell me what is the best method to use to solve this question?

Easier to apparch this as backward problem..

Let the total number of coins at the end = 100u

so at the end,

50 cent coins = 40u,
20 cent coins = 30u,
10 cent coins = 30u

Then at the beginning,

10 cent coins = 5/2 (30u) = 75u
20 cent coins = 4/3(30u) = 40u
50 cent coins = 40u + 18

75u = 40u + 18 + 24---> 35u = 42---> u = 6/5

10 cent coins in beginning = 75(6/5) = 90

question (b) follows easily from thereon..

[EnglishZaiMathsHaiz]

The Ans for question 16 is A)11 B)31 . I used algebra

[Vanilla Cake]

Hi Uncle Dharma/Uncle Tianzhu,

Good morning, Uncles. Could you pls spare your precious time to look into Q17 (c) from PSLE 2010 Maths exams paper 2 set on 07 Oct 2010 (Thursday) and advise accordingly? TIA.

Q17 (not in exact words)
Structure Number  Number of Rods  Height (cm)\t\t\t\t\t
-------------------------------------------------------------\t\t\t\t\t
            1                        12                      3\t\t\t\t\t
            2                        20                      3\t\t\t\t\t
            3                        25                      6\t\t\t\t\t
            4                        33                      6\t\t\t\t\t
            5                        38                      9\t\t\t\t\t
            6\t\t\t\t\t
-------------------------------------------------------------\t
a) Fill in the number of of rods and height for structure 6. [1 mark]
b) Find the height of Structure 119. [2 marks]
c) Find the number of rods for Structure 119. [2 marks]

For part (a) should be 46 rods and 9 cm and part (b) should be 180 cm.
How about part (c)? Is it 779 rods or 782 rods?

Congratulations for an easy PSLE 2010 Maths exam papers for most P6 students.
Oh dear, next year's PSLE 2011 Maths exam papers may be difficult for my younger sister.