Q&A - PSLE Math
-
Vanilla Cake:
Good morning 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.
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
Sometimes a difficult paper maybe a blessing in disguise because PSLE aggregate is calculated based on sum of the T-scores of the 4 papers. A very easy paper can be very damaging to a pupil who has made a few careless mistakes, where for every 1 mark lost in the raw score will result in a comparatively larger drop in the T-score. -
Dharma:
Hi Mr. Dharma,
Sometimes a difficult paper maybe a blessing in disguise because PSLE aggregate is calculated based on sum of the T-scores of the 4 papers. A very easy paper can be very damaging to a pupil who has made a few careless mistakes, where for every 1 mark lost in the raw score will result in a comparatively larger drop in the T-score.
You are absolutely correct.
In my view, an easy paper especially hurts students who have prepared very well for Maths and also students who are naturally proficient in Maths. Moreover, when the paper is very easy, students who are prone to careless mistakes, pay a heavy price in T-score damage. Not many realise this.
Thank you very much for your valuable insight. -
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. -
Apologies to disappontyou. Pattern 3 is 28 rods
-
I’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. -
the kiasu student:
Can some one post the PSLE 2010 Math MCQ questions? I nid the questions( not answers ) so that i can check hw many marks i got. Pls help me!!!!
Question 2, a giveaway.
This question is set simply.
Which of the following is the largest?
Without looking at the hundredth and thousandths place, we can already get the answer.
The one with the 0.2-- is the answer.
Question 13: The figure below is made up of identical equilateral triangles of sides 3cm. How many triangles will there be if the perimeter of the figure is 93cm?
The 2 common answers are 29 and 31, (2) and (4) respectively.
(2) is correct because 93-6=87 87/3=29
(4) is due to careless because the pupil may have forgotten the 2 ''extra\" 3cm(s) at both ends of the figure. -
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:
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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