Q&A - PSLE Math

[tianzhu]

leesf:

Q3) A street-lamp is erected at an interval of 8m on one side of the street. On the other side of the street, an angsana tree is planted at every 6m. There are 12 more angsana trees than street-lamps.
a) Ho long is the street if there is one street-lamp and one angsana tree on both ends of the street.
b) How many street-lamps and angsana trees are there?

Hi

This question is quite similar to the balloon question in PSLE Maths 2009.

String of 2 big balloons is 90cm
String of 5 small balloons is is 1.2m
If both strings are of the same length, there would be 105 more small balloons than the big balloons. How many balloons are there altogether?

Best wishes

[Dharma]

Q3) A street-lamp is erected at an interval of 8m on one side of the street. On the other side of the street, an angsana tree is planted at every 6m. There are 12 more angsana trees than street-lamps.

a) How long is the street if there is one street-lamp and one angsana tree on both ends of the street.
b) How many street-lamps and angsana trees are there?

Spacing ratio => Street lamp : Angsana Tree = 4u : 3u = 4 : 3
Qty ratio => Street lamp : Angsana Tree = 3u + 1 : 4u + 1

(4u + 1 ) – (3u + 1 ) = 1u = 12
Length of street = (3x12) x 8m = 288m or (4 x 12) x 6 = 288m

No. of street lamps = (3 x 12) + 1= 37
No. of angsana trees = (4 x 12) + 1 = 49

[Dharma]

pecalis:

Thanks Dharma,
For sharing the solutions and the clear explanation. Really appreciate it

Glad u like it.

[tianzhu]

Hi


Hope this helps.

Best wishes.

http://farm5.static.flickr.com/4153/5031778629_5f8363e5c4_b.jpg\">

[octopusmum]

Hi Vanilla cake

thks for telling me the solutions for the 2 maths questions. i simply did not have the time to search for the answers myself so have to trouble kind souls like you to help…

i need help again with the following question from Henry Park maths 2010 prelim paper. it is qtn 11 in paper 2:

The figure shows an empty tank. It is made from 2 containers. The containers are in the form of 2 cubes of sides 8 cm and 20 cm respectively. The small container is attached to the centre of one of the sides of the big container. 4 litres of water is poured into the big container such that water flows in to fill part of the small container. What is the height of the water level in the big container? Round off your answer to 2 decimal places.

it is easier to see the question with the diagram but i am not able to reproduce the diagram here…if you or anyone else happen to know the solution or know where to get the detailed solution, pls share.

thks v much

a very desperate and exhausted octopusmum

[kancheongmum]

octopusmum:

Hi Vanilla cake

thks for telling me the solutions for the 2 maths questions. i simply did not have the time to search for the answers myself so have to trouble kind souls like you to help...

i need help again with the following question from Henry Park maths 2010 prelim paper. it is qtn 11 in paper 2:

The figure shows an empty tank. It is made from 2 containers. The containers are in the form of 2 cubes of sides 8 cm and 20 cm respectively. The small container is attached to the centre of one of the sides of the big container. 4 litres of water is poured into the big container such that water flows in to fill part of the small container. What is the height of the water level in the big container? Round off your answer to 2 decimal places.

it is easier to see the question with the diagram but i am not able to reproduce the diagram here..if you or anyone else happen to know the solution or know where to get the detailed solution, pls share.

thks v much

a very desperate and exhausted octopusmum

Hi octopusmum

I take the liberty to help you with this question as DS also need help.
The basic concept is volume = L x B x H
what is L x B? Is the base area right. So keep this in mind
Total volume water 4L = 4000 cm3
volume of water below 8 cm cube = 20 x 20 x 6 ((20 - 8/2))=2400cm3
the remaining water above the 8cm cube will have different base area.
= 4000 - 2400 = 1600cm3
new base area is (20x20) + (8x8)= 464 cm2
vol of remaining water divide by this new base area you will get the height. 1600/464 = 3.45 cm
3.45 + 6 = 9.45 cm

Nanyang prelim 2010 Q11 is almost the same as above question. You may want to let your child try.

Let us know if you need help.

[Vanilla Cake]

octopusmum:

i need help again with the following question from Henry Park maths 2010 prelim paper. it is qtn 11 in paper 2:


The figure shows an empty tank. It is made from 2 containers. The containers are in the form of 2 cubes of sides 8 cm and 20 cm respectively. The small container is attached to the centre of one of the sides of the big container. 4 litres of water is poured into the big container such that water flows in to fill part of the small container. What is the height of the water level in the big container? Round off your answer to 2 decimal places.

Do take note that the diagram is not the original diagram as printed in the original question.

Refer to http://psle2010a.blogspot.com/2010/09/figure-shows-empty-tank.html

OR

from another helpful soul in OnSponge forum:

(20-8)cm/2 = 6cm\t\t\t\t
6cm x 20cm x 20cm = 2400cm³ (cubic centimetre)\t\t\t\t
\t\t\t\t
4 litres = 4000cm³\t\t\t\t
4000cm³ - 2400cm³ = 1600cm³\t\t\t\t
\t\t\t\t
1cm x 8cm x 8cm + 1cm x 20cm x 20cm = 464cm³\t\t\t\t
(1600cm³ / 464cm³/cm) + 6cm = 9.45cm (correct to 2 d.p.)\t

PS: I can understand your feelings as I took PSLE in 2008 and my younger sister will be taking PSLE in 2011.

[Dharma]

tianzhu:

leesf:

Q3) A street-lamp is erected at an interval of 8m on one side of the street. On the other side of the street, an angsana tree is planted at every 6m. There are 12 more angsana trees than street-lamps.
a) Ho long is the street if there is one street-lamp and one angsana tree on both ends of the street.
b) How many street-lamps and angsana trees are there?

Hi

This question is quite similar to the balloon question in PSLE Maths 2009.

String of 2 big balloons is 90cm
String of 5 small balloons is is 1.2m
If both strings are of the same length, there would be 105 more small balloons than the big balloons. How many balloons are there altogether?

Best wishes

2 big ballons at every 90cm of string.
1 big balloon => 45cm

5 small ballons at every 120cm of string
1 small balloon => 24cm

Ratio of length => Small : Big = 8 : 15
Ratio of qty => Small : Big = 15 : 8

15u – 8u = 105
7u = 105
1u = 15
Total no. of balloons = 23u = 23 x 15 = 345

[kancheongmum]

Hi all this question is from RGS 2010 prelim Q18

I believe it had been posted before in this forum and by Observer. Here is another suggested solution done by my DS which I find very simple and easy the understand. I have taught him to draw model like this for this type of question as he not good at doing the usual model. I have seen solutions provided by sponge forum with complicated models and workings which myself and some of you find difficult to understand. I hope this can help.

There are more pupils in School A than School B. 30% of the pupils in School A is 45 more than 40% of the pupils in School B. If 10% of the pupils in School A leaves to join School B, there will be 200 more pupils in School A than School B.
(a) How many pupils are there in School B?
(b) How many percent less pupils are there in School B than School A?
Leave your answer as fraction in the simplest form.


30% ----3/10 40% ----2/5
equal fraction 3/10 — 6/20 (school A) 2/5 ---- 6/15 (school B)

from the equal fraction we compare A & B:
School A — total 20u + 150
for every 6u of A there is 45 more, 2u there is 15 more

School B ---- total 15u

with the above we can draw the model for better visual of the equation

At First:
School A
()()15
()()()()()()45
()()()()()()45
()()()()()()45
total: 20u + 150

School B
()()()()()()
()()()()()()
()()()
total: 15u

10% move from A to B, ()()15 shift from A to B
then there are 200 more pupils in School A

18u + 135 = 17u + 15 + 200
1u = 80
(a) pupils in School B 80 x 15u = 1200 pupils
(students please note that this is a "if " question so there is no actual transfer. I always highlight to my DS as he is very careless. Underline the word "if" to remind yourself)

(b) Pupils in School A = (80 x 20u) + 150 = 1750
1750 - 1200 = 550
(550/1750) x 100% = 31 3/7 %

Best wishes to all sitting for PSLE.

[Muffins]

Vanilla Cake:

PS: I can understand your feelings as I took PSLE in 2008 and my younger sister will be taking PSLE in 2011.

Good luck in advance to your DSis!!! for an all A* clean sweep :xedfingers: