Q&A - PSLE Math
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yongjianrong:
Hi jianrongI'm Jian Rong on onsponge, the place where you got the info, apologies for the mistake.
It's 28 rods, followed by 33, 41 then 46.
Good Morning
You’ve done a great job in coming up with a list of answers and questions after PSLE Maths.
I must say I am amazed by your ability to remember so much under stressful examination conditions.
Probably about 50000 students took the test on 7 October 2010.But you are the only one who took the trouble to come up with such a comprehensive list.
We, in KSP forum, appreciate the extra efforts you put in.
May you be blessed with a successful PSLE 2010.
Best wishes -
Vanilla Cake:
(a)tianzhu:
![](\"http://farm5.static.flickr.com/4146/5061961412_3b05b3d38d_b.jpg\")
http://farm5.static.flickr.com/4146/5061961412_3b05b3d38d_b.jpg\">
Dharma:
According to http://www.onsponge.com/forum/35-thinkingmathonsponge/5790-how-did-you-do-psle-math-2010.html?limit=10&start=30#5857, pls refer to the revised numbers as below:Q17 ( c )
119 is an odd number.
We can establish a pattern for the number of rods for Structure Numbers that are odd numbers.
Structure 1=> 12 rods = (12 x 1) + 0
Structure 3 => 25 rods = (12 x 2) + 1
Structure 5 => 38 rods = (12 x 3 ) + 2
Structure 7 => 51 rods = ( 12 x 4) + 3
.
.
.
Structure N => [12(N + 1)/2 ] + (N – 1)/2
So,
Structure 119 => 12(120/2) + (118/2) = 779 rods
Structure Number Number of Rods Height (cm)\t\t\t\t
--------------------------------------------------------------\t\t\t\t
1 12 3\t
2 20 3\t
3 28 6\t
4 33 6\t
5 41 9\t
6 ? ?\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]
Uncle Tianzhu, could you pls edit or repost the new solution based on the new set of numbers?
Uncle Dharma, could you also edit or repost the new solution based on the new set of numbers from part (a) to part (c)?
I think this should be the right set of numbers to arrive correct answers as:
(a) 46 rods and 9 cm (b) 180 cm (c) 782 rods.
Thank you to both Uncles for your continued support and time.
To find the number of rods [R] & Height of structure [H]
Structure 1 ; R = 12 ; H = 3
Structure 2 ; R = 12 + 8 = 20 ; H = 3
Structure 3 ; R = 20 + 8 = 28 ; H = 6
Structure 4 ; R = 28 + 5 = 33 ; H = 6
Structure 5 ; R = 33 + 8 = 41 ; H = 9
Structure 6 ; R = 41 + 5 = 46 ; H = 9
(b)
Structure No. => Odd
Structure N => H = (N + 1)/2 x 3
Structure 119 => (119 + 1)/2 x 3 = 60 x 3 = 180
Height of Structure 119 = 180cm
(c)
Structure No. => Odd
Structure 3 ; R = 28 + ( 13 X 0 )
Structure 5 ; R = 28 + ( 13 X 1 )
Structure 7; R = 28 + ( 13 X 2 )
.
.
.
Structure N ; R = 28 + [ 13 x (N- 3)/2]
Structure 119 ; R = 28 + [13 x (119 – 3)/2 ] = 782
No. of rods for Structure 119 = 782 -
Dharma:
(a)Vanilla Cake:
[quote=\"tianzhu\"]
Dharma:
According to http://www.onsponge.com/forum/35-thinkingmathonsponge/5790-how-did-you-do-psle-math-2010.html?limit=10&start=30#5857, pls refer to the revised numbers as below:Q17 ( c )
119 is an odd number.
We can establish a pattern for the number of rods for Structure Numbers that are odd numbers.
Structure 1=> 12 rods = (12 x 1) + 0
Structure 3 => 25 rods = (12 x 2) + 1
Structure 5 => 38 rods = (12 x 3 ) + 2
Structure 7 => 51 rods = ( 12 x 4) + 3
.
.
.
Structure N => [12(N + 1)/2 ] + (N – 1)/2
So,
Structure 119 => 12(120/2) + (118/2) = 779 rods
Structure Number Number of Rods Height (cm)\t\t\t\t
--------------------------------------------------------------\t\t\t\t
1 12 3\t
2 20 3\t
3 28 6\t
4 33 6\t
5 41 9\t
6 ? ?\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]
Uncle Tianzhu, could you pls edit or repost the new solution based on the new set of numbers?
Uncle Dharma, could you also edit or repost the new solution based on the new set of numbers from part (a) to part (c)?
I think this should be the right set of numbers to arrive correct answers as:
(a) 46 rods and 9 cm (b) 180 cm (c) 782 rods.
Thank you to both Uncles for your continued support and time.
To find the number of rods [R] & Height of structure [H]
Structure 1 ; R = 12 ; H = 3
Structure 2 ; R = 12 + 8 = 20 ; H = 3
Structure 3 ; R = 20 + 8 = 28 ; H = 6
Structure 4 ; R = 28 + 5 = 33 ; H = 6
Structure 5 ; R = 33 + 8 = 41 ; H = 9
Structure 6 ; R = 41 + 5 = 46 ; H = 9
(b)
Structure No. => Odd
Structure N => H = (N + 1)/2 x 3
Structure 119 => (119 + 1)/2 x 3 = 60 x 3 = 180
Height of Structure 119 = 180cm
(c)
Structure No. => Odd
Structure 3 ; R = 28 + ( 13 X 0 )
Structure 5 ; R = 28 + ( 13 X 1 )
Structure 7; R = 28 + ( 13 X 2 )
.
.
.
Structure N ; R = 28 + [ 13 x (N- 3)/2]
Structure 119 ; R = 28 + [13 x (119 – 3)/2 ] = 782
No. of rods for Structure 119 = 782[/quote]
actually i did it this way
theres a formula for any odd numbered figure that is higher than 1 eg. picture3,5,7,9 etc.
the formula is: 6.5n+8.5
where n is the number of the odd numbered figure that is higher than 1 -
Hi VC
I believe there are diagrams provided in Q17.
The first slide helps to explain the addition of rods to form the structures.
Hope this helps.
Best wishes.![](\"http://farm5.static.flickr.com/4152/5064543276_48eb65032a_b.jpg\")
![](\"http://farm5.static.flickr.com/4087/5063710027_2d395557a8_b.jpg\")
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tianzhu:
Hi Uncle Tianzhu,Hi VC
I believe there are diagrams provided in Q17.
The first slide helps to explain the addition of rods to form the structures.
Hope this helps.
Best wishes.
Yes, it really helps a lot! Thanks and you must have spent quite some time drawing out these figures and presenting them.
As you are aware that not all the past years' PSLE Maths questions are available in the published 5-year series, that's why I am compiling the questions and solutions for PSLE Maths 2010 exam from online forums/discussions..
My younger sister shuddered to think of facing a daunting/difficult PSLE Maths 2011 exam that caused her blood to run cold and send shivers down her spine.She definitively has to put in more effort to pull through.
-
Vanilla Cake:
Hi VC
Yes, it really helps a lot! Thanks and you must have spent quite some time drawing out these figures and presenting them.
As you are aware that not all the past years' PSLE Maths questions are available in the published 5-year series, that's why I am compiling the questions and solutions for PSLE Maths 2010 exam from online forums/discussions..
Good Morning.
You’re welcome. I am glad you liked it.
Yes, it took some time; my wife complained I looked more at the MD than at her.
Your compilation of past years questions may be very useful for future kiasu kids, maybe you could call it ----- Vanilla Cake’s way to excel in PSLE Maths.
Don’t worry too much, your sister should do well next year.
Best wishes -
iFruit:
Thanks! That certainly is faster and neater than what I've come up with!
Easier to apparch this as backward problem..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?
Let the total number of coins at the end = 100u -
Kumar spent $1729 on a set of encyclopedia. He spend 1/4 of the remainder on a camera and still had 2/5 of his money left. Find the total amount of money he had at first. - (sorry some amendment)
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mumthebest:
Kumar spent $1729 on a set of encyclopedia. He spend 1/4 of the remainder on a camera and still had 2/5 of his money left. Find the total amount of money he had at first. - (sorry some amendment)
Let the remainder after buying encyclopedia = 20u
Monet spent on camera = 5u
Money left = 15u
5u+1729---> 3/5 of money
15u---> 2/5 of money
2(5u+1729) = 3(15u)
35u = 1729x2--->5u = 247x2
total money = 1729+20u = 1729 + 4x247x2 = 3705 -
iFruit:
The model answer is $3705mumthebest:
Kumar spent $1729 on a set of encyclopedia. He spend 1/4 of the remainder on a camera and still had 2/5 of his money left. Find the total amount of money he had at first. - (sorry some amendment)
Let the remainder after buying encyclopedia = 20u
Monet spent on camera = 5u
Money left = 15u
5u+1729---> 3/5 of money
15u---> 2/5 of money
2(5u+1729) = 3(15u)
5u = 1729x2
total money = 1729+20u = 1729 + 4x1729x2 = 9x1729
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