Q&A - PSLE Math

[tianzhu]

Belle2011:

Dear tianzhu,

I can understand better the above method of yours.
I am always struggling very hard on this type of problems.
Thanks very, very much for your time and effort spent for helping me and others.

Cheers,
Belle.

Hi Belle2011

You’re welcome.

Best wishes

[tianzhu]

Leanne:

Hi Tianzhu,

Today,u post some beautiful pic of model and that brighten up the pc screen.Thanks

Check with you, ds loves to use model to solve almost every question, if not its ratio method.May I know how do we know the question is not suitable to use model method as it becomes tedious, is there a way to identify it?Also, how to avoid misread in questions for model?Like sometime, to a kid, this I means Ali but it actually mean daniel .thanks

Cheers
Leanne

Hi Leanne

You’re welcome.

First as a parent, I felt inadequate to answer your questions as my experience is only limited to one kid. An educator would be in a better position to address your issues.

Nevertheless, I’ll attempt to answer your queries basing on my experience in my maths journey with my boy.

We must recognise that MD is one of many heuristics or problem solving strategies in the primary maths syllabus. It’s not the only method. It’s always good to expose kids to a variety of methods and let them select the method they are most comfortable with to solve a particular question.

MD helps kids to \"see\" Maths, but there may be situations where the numbers given in the questions may make it more challenging to use it.

According to this book, Challenging Maths Problems Made Easy, if the questions involve “more than” or “less than” type, MD is more suitable. If the questions involve ratios, fractions and percentages in two cases, the Units Method would be preferred.

I think I’ve mentioned in some earlier posts, my kid preferred to use Units Method (Units and Parts) for questions involving two changed quantities (Please refer to Belle 2011’s question).MD can also be used for such questions, however, UM may be more efficient.

We usually start with some form of simple representation to show the relationships between the before and after scenarios, As my kid got more familiar with the Units Method, he then could have the option of not drawing the diagram and proceeded directly to use the Units Method.

As for carelessness, I think it’s something all students in the world are capable of making. What I did in my boy’s case was to sit down with him and count the number of marks lost due to carelessness in his test papers. Hopefully he would feel “heart pain” and be more careful in future tests.

Hope this helps.

[Belle2011]

Dear \"si-fus\",

In a class, 40% of pupils wore glasses. After 5 pupils who wore glasses left the class, the percentage of pupils who wore glasses dropped to 30%. How many pupils in the class did not wear glasses?

To help myself:
40% wear glasses ie 2/5 wear glasses.
This means 60% of the pupils do not wear glasses ie 3/5 not wearing glasses.

After 5 pupils who wore glasses left, the % of pupils who wore glasses dropped to 30%. Now my question is this 30% : does this 30% mean
(new number of pupils wearing glasses ) / (new total number of pupils) ???

I know the number of pupils not wearing glasses DID NOT change in this case.

I cannnot solve !

Thank-you.

Cheers,
Belle.

[Brenda10]

Belle2011:

Dear \"si-fus\",

In a class, 40% of pupils wore glasses. After 5 pupils who wore glasses left the class, the percentage of pupils who wore glasses dropped to 30%. How many pupils in the class did not wear glasses?

To help myself:
40% wear glasses ie 2/5 wear glasses.
This means 60% of the pupils do not wear glasses ie 3/5 not wearing glasses.

After 5 pupils who wore glasses left, the % of pupils who wore glasses dropped to 30%. Now my question is this 30% : does this 30% mean
(new number of pupils wearing glasses ) / (new total number of pupils) ???

I know the number of pupils not wearing glasses DID NOT change in this case.

I cannnot solve !

Thank-you.

Cheers,
Belle.

Hi Belle

DD would like give a try:

3/5 = 7/10
21/35 = 21/30

At first : 35 After: 30

3/5 x 35 = 21

or another method

At first
W: WO
2:3 = 14 : 21

After
W:WO
3:7 = 9: 21

Hopefully the answer is correct.

[anneshirleygilbert]

Hello Tianzhu,


I’m referring to the other method. I think you call it the Units Method where the initial number of units for $100 notes became 112 units. Why do you multiply by 16 for all the numbers on the $100 side. i don’t see the rationale… but this method does help you get the right answer.

I hope you know what I mean. I see many such questions in my daughter’s worksheets. If I can understand and explain this method to her, I think she’d hurdle quite a huge obstacle.

Thanks in advance.

[Belle2011]

Brenda10:

3/5 = 7/10

21/35 = 21/30

At first : 35 After: 30

3/5 x 35 = 21

or another method

At first
W: WO
2:3 = 14 : 21

After
W:WO
3:7 = 9: 21

Hopefully the answer is correct.

Yes, the answer of 21 is CORRECT.
Thank-you for sharing.

Cheers,
Belle.

[tianzhu]

anneshirleygilbert:

Hello Tianzhu,


I'm referring to the other method. I think you call it the Units Method where the initial number of units for $100 notes became 112 units. Why do you multiply by 16 for all the numbers on the $100 side. i don't see the rationale... but this method does help you get the right answer.

I hope you know what I mean. I see many such questions in my daughter's worksheets. If I can understand and explain this method to her, I think she'd hurdle quite a huge obstacle.

Thanks in advance.

Hi anneshirleygilbert

You are referring to the first solution where the ratios are based on the number of notes.

In this question, Angel exchanged 12 pieces of $100 into some $5 notes. Hence, 12 pieces of $100 notes or $1200 is changed into 240 pieces of $5 notes. Therefore, the number of notes in the beginning and the end are different.

To enable us to make a comparison, we make the final quantities (1 part and 16 parts) equal. That’s why we multiply the left column ($100 notes) by 16. In the second table, notice that the final ratios are equal (16 parts).

Hope this helps.

Best wishes

[Brenda10]

Belle2011:

Yes, the answer of 21 is CORRECT.
Thank-you for sharing.

Cheers,
Belle.

Hi Belle

You're welcome.

[anneshirleygilbert]

tianzhu:

anneshirleygilbert:

Hello Tianzhu,


I'm referring to the other method. I think you call it the Units Method where the initial number of units for $100 notes became 112 units. Why do you multiply by 16 for all the numbers on the $100 side. i don't see the rationale... but this method does help you get the right answer.

I hope you know what I mean. I see many such questions in my daughter's worksheets. If I can understand and explain this method to her, I think she'd hurdle quite a huge obstacle.

Thanks in advance.

Hi anneshirleygilbert

You are referring to the first solution where the ratios are based on the number of notes.

In this question, Angel exchanged 12 pieces of $100 into some $5 notes. Hence, 12 pieces of $100 notes or $1200 is changed into 240 pieces of $5 notes. Therefore, the number of notes in the beginning and the end are different.

To enable us to make a comparison, we make the final quantities (1 part and 16 parts) equal. That’s why we multiply the left column ($100 notes) by 16. In the second table, notice that the final ratios are equal (16 parts).

Hope this helps.

Best wishes[/quote

Thank you, tianzhu. Got it now.... it's simply \"to enable us to make a comparison\". What an ingenious way to get the answer! Thanks a bunch! I've been very impressed with the heuristic approach to answering P5/6 math questions.]

[tianzhu]

anneshirleygilbert:

Thank you, tianzhu. Got it now.... it's simply \"to enable us to make a comparison\". What an ingenious way to get the answer! Thanks a bunch! I've been very impressed with the heuristic approach to answering P5/6 math questions.]

Hi anneshirleygilbert

You're welcome.

Best wishes