Q&A - PSLE Math

[tianzhu]

Treelodge:

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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

[tianzhu]

charsen:

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

Hi

Thank you for pointing out my error.

24 units – 105 -------- 9 units + 30 (3/8 of 24 units + 80).

15 units -------- 135

1 unit ------- 9

I’ll revise my earlier solution.

Best wishes

[Winx5015]

Please help !!!


(1). In an enrichment class of 48 students, each student must take at least a language class or a mathematics class. 7/12 of the students choose French language and 1/4 of the students choose French language and a mathematics class. How many students choose only a mathematics class?

(2). Mrs Tan bought 3kg of strawberries and 8kg of grapes. Mrs Chin bought 3kg of grapes and 8kg of strawberries. Mrs Chin spent $35 more than Mrs Tan. If 1kg of grapes cost $8, how much would 1kg of strawberries cost?

(3). There were 180 apples and 240 oranges in Box A. There were 400 apples and 120 oranges in Box B. How many apples and how many oranges must be transferred from Box B to Box A such that 50% of the fruits in Box A and 3/4 of the fruits in Box B are apples?

(4). Mr Ramy walks from his house to his office every morning. If he walks at a speed of 65m/min, he will be late for work by 5 minutes. If he increases his speed by 15m/min, he will be early for work by 4 minutes. How far is his office from his house?

Thanks you

[charsen]

Help needed for this question.

A class of 40 pupils took part in a test.Each pupil was given the same number of questions to answer in the test.5 marks were awarded for each correct answer.3 marks were deducted for each wrong answer.No marks was awarded or deducted for any question not attempted.
For every 21 questions,2 questions were not attempted and 7 questions were answered wrongly.The class scored a total of 6240 marks for the test.How many questions were there on the test paper?

[tianzhu]

charsen:

Help needed for this question.

A class of 40 pupils took part in a test.Each pupil was given the same number of questions to answer in the test.5 marks were awarded for each correct answer.3 marks were deducted for each wrong answer.No marks was awarded or deducted for any question not attempted.
For every 21 questions,2 questions were not attempted and 7 questions were answered wrongly.The class scored a total of 6240 marks for the test.How many questions were there on the test paper?

Hi

First consider a set of 21 questions.

2 wrong questions ------ nil marks

7 wrong questions ------- 7*3 -------- 21 marks deducted

12 correct answers -------- 12*5 ------- 60 added

Hence 60 -21 ------39 marks for a set of 21 questions.

6240/39 -------- 160

Number of questions -------- 160*21 ------- 3360

Number of questions per testpaper --------- 3360/40 ------- 84

Best wishes

[tianzhu]

Winx5015:

Please help !!!

(1). In an enrichment class of 48 students, each student must take at least a language class or a mathematics class. 7/12 of the students choose French language and 1/4 of the students choose French language and a mathematics class. How many students choose only a mathematics class?

Hi

Please take a look at the solution for a similar type of question.

Best wishes

http://farm8.staticflickr.com/7243/6966119100_e47f2d8176_z.jpg\">

[tianzhu]

Winx5015:

(4). Mr Ramy walks from his house to his office every morning. If he walks at a speed of 65m/min, he will be late for work by 5 minutes. If he increases his speed by 15m/min, he will be early for work by 4 minutes. How far is his office from his house?

Hi

65*5 -------- 325

80*4 ------- 320

325 + 320 ------- 645

645/15 ------- 43 min

Distance ------- 43*65 + 325 -------- 3120m or 43*80 – 320 ------- 3120m

Best wishes

[tianzhu]

Winx5015:

(3). There were 180 apples and 240 oranges in Box A. There were 400 apples and 120 oranges in Box B. How many apples and how many oranges must be transferred from Box B to Box A such that 50% of the fruits in Box A and 3/4 of the fruits in Box B are apples?

Hi

There are many examples of similar types of questions in this thread.

There are a few approaches, using pictorial way, Units and Parts or letters of the alphabet.

Here’s an example using MD, you may also use U and P to replace the boxes and circles.

Best wishes

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