Q&A - PSLE Math

[tianzhu]

jewelbox:

Appreciate any help on this qn (RGS SA1 2012) : http://i49.tinypic.com/i1invc.jpg\">

Hi

Good Morning.

I don’t have time for slide now.

QRS is an isosceles triangle.

Similarly, QRU is also an isosceles triangle.

Angle UQR ------- 53 degrees.

Best wishes

[kay22]

Angelina and Smanatha took part in a cross country race. Angelina ran at a speed of 20 m/s. Both did not change their speed throughout the race. When Angelina covered 2/3 of the distance and Samantha covered 3/4 of the distance, they were 250m apart. what was Samantha's running speed?


:scratchhead:

[kay22]

Angelina and Smanatha took part in a cross country race. Angelina ran at a speed of 20 m/s. Both did not change their speed throughout the race. When Angelina covered 2/3 of the distance and Samantha covered 3/4 of the distance, they were 250m apart. what was Samantha’s running speed?

[jewelbox]

Thanks Tianzhu… i got it.

[Zhu99]

kay22:

Angelina and Smanatha took part in a cross country race. Angelina ran at a speed of 20 m/s. Both did not change their speed throughout the race. When Angelina covered 2/3 of the distance and Samantha covered 3/4 of the distance, they were 250m apart. what was Samantha's running speed?

2/3 = 8/12

3/4 = 9/12

8 u --> 20 m/s [As time is the same for both]

9 u ---> 20/8 x 9 = 22.5 m/s

Samantha's running speed was 22.5 m/s.


Or

2/3 = 8/12

3/4 = 9/12

9 - 8 = 1 u ---> 250 m

8 u ---> 250 x 8 = 2000 m --- Distance of A

9 u ---> 250 x 9 = 2250 m --- Distance of S

2000/20 = 100 s --- Time of A to cover 2000 m

2250/100 = 22.5 s

Samantha's running speed was 22.5 m/s.

[2DMommy]

Please assist


There are more students in School A than in School B. 30% of the students in School A is 45 more than 60% of the students in School B. If 10% of the students in School A leave to join School B, there will be 210 more pupils in School A than School B.
a) How many students are there in School B?
b) How many per cent less students are there in School B than in School A?

Thank you!

[Zhu99]

jewelbox:

Appreciate any help on this qn (RGS SA1 2012) : http://i49.tinypic.com/i1invc.jpg\">

180 - 37 - 12 - 25 = 106 --- Angle URT

180 - 106 - 37 = 37 --- Angle USR

RU = RS since Angle RUS = Angle URS [Isosceles triangle]

Since RU = QR, ARU is also an isosceles triangle

106/2 = 53

Angle UQR is 53 degree.

[tianzhu]

Treelodge:

http://i50.tinypic.com/54yk9l.jpg\">

Hi

This is an interesting question from the latest SA2 papers.

It looks intimidating at first glance.

There is not much information in it.

Actually, all one needs is covered in the school syllabus.

The line FC divides the square ABDE into two rectangles of different sizes.

The underlying concept is a rectangle having the same base and height as a triangle has twice the area of the triangle.

If a student is able to see this concept, the rest of the calculations is pretty neat.

I’ve attempted to post a slide last Sunday, unfortunately was unable to do so due to some technical issue.

Hope this helps.

Best wishes

http://farm9.staticflickr.com/8321/7978766554_70b139f8ba_z.jpg\">

[tianzhu]

2DMommy:

Please assist


There are more students in School A than in School B. 30% of the students in School A is 45 more than 60% of the students in School B. If 10% of the students in School A leave to join School B, there will be 210 more pupils in School A than School B.
a) How many students are there in School B?
b) How many per cent less students are there in School B than in School A?

Thank you!

Hi

A neat way is use MD. You may also use UM.

Draw 3 boxes to show 60% of the students in School B.Therefore,100% of school B ------- 5 boxes.

30% of the students in school A ------ 3 boxes + 45.Draw 1 box +15 to show 10% of students in school A.

Therefore 100% ------ 10 boxes + 150

If 10% of the students in School A leave to join School B, there will be 210 more pupils in School A than School B.

After the transfer

A -------- 9 boxes + 135

B -------- 6 boxes + 15

9 boxes + 135 -------- 6 boxes + 15 + 210

3 boxes ------- 90

1 box ------- 30

You may carry on from here.

Best wishes

[charsen]

tianzhu:

peggy:

Kindly assist.



A number of passengers boarded an empty MRT train at pasir ris station.

At Tampines station, 2/5 of them alighted and 80 boarded the train.
At Simei station, 223 alighted and 38 boarded the train.
The train now has 3/8 of the number of passengers when it left Tampines station.

A. How many passengers were on the train when it left Simei station?
B. How many passengers were on the train when it left Pasir Ris station?

Thank you.

Hi

Good Morning.

You may use MD or work with units.

It helps to have a simple diagram to show the flow of events.

The number of passengers leaving one station is the same as the number of passengers arriving at the next station.

Pasir Ris -------- 40 units

Tampines

At first -------- 40 units

2/5 of them alighted and 80 boarded the train.

Alighted ------- 16 units

Left ------- 24 units + 80

Simei

At first ------- 24 units + 80

223 alighted and 38 boarded the train.

Left -------- 24 units + 80 - 223 + 38 -------- 24 units – 105

The train now has 3/8 of the number of passengers when it left Tampines station.

24 units – 105 -------- 15 units + 30 (3/8 of 40 units + 80)

1 unit ------ 15

a)Number of passengers leaving Simei station ------- 15*15 + 30 -------- 255

b)Number of passengers leaving Pasir Ris station ------- 40*15 ------- 600.

Best wishes

Dear Tianzhu,
I have noticed a mistake in your workings.For the part where they said the no.of passengers in the end is 3/8 of the no.of passengers in the train leaving tampines. Thus,(24u-105)/3 x8=64u-280.
64u-280=24u+80.It is not 3/8 of 40.
Cheers