Q&A - PSLE Math

[tianzhu]

Hi VC


It’s nice to hear from you.

The question posed by livewith_vanilla is an interesting one. Unlike more familiar questions involving two changed quantities, the number (124) involved in the transaction is in one single lot.

Usually questions involving two changed quantities can be solved by Units and Parts, Model Drawing or equivalent ratios where numbers are presented in a tabulated list.

In this particular question, MD is out. If you try to use UP, you’ll also face obstacles. I also hit the dead end trying to get the answer. However, if you try to use equivalent ratios, you’ll be able to get the answer of 26 based on the context in the question.I am not sure if this is the actual question from any test papers or books or just an example given by livewith_vanilla.As such, there may be multiple answers.

Best wishes

[CoffeeCat]

Mr tianzhu, is your equivalent ratio method the one where you make two listings of multiples of 13 and 5 separately and pick the first 2 which has a difference of 124?


I agree that this question is too vague ( so multiple solutions existed). Perhaps a sentence should be added saying that only the lowest answer is required.
On the other hand, until livewithvanilla elaborate more, I will think that it is highly unlikely that such a question actually appeared as a homework question for p6. It is my guess that she is trying to illustrate a quick example of questions involving 2 changed quantities.
In any case I look forward to hearing from livewithvanilla the simple method=).

[tianzhu]

Hi Coffeecat


I guess you are a coffee lover.

Let’s hold our curiosity for a while and wait for livewith_vanilla to come back with the actual question next week.Her question is pretty unique as compared to the usual question concerning two changed quantities.

And yes, you are correct, just make a list.

Best wishes

[tianzhu]

Hi


While waiting for livewith_vanilla to come back with her question, I would like to put up two familiar types of questions concerning two changed quantities types of questions. Questions of this genre can be solved using Units and Parts, Model Drawing or Making a list (Equivalent ratio).

You may want to compare them with the question from livewith_vanilla to see the difference.

1)The ratio of Ryan’s pocket money to John’s pocket money was 3 : 2. After Ryan saved $15 and John spent $8, the ratio of Ryan’s pocket money to John’s pocket money was 3 : 1. How much money did Ryan have at first?

2) The number of Malvin’s stamps to Ken’s stamps was 2:3. After Malvin bought another 8 stamps and Ken lost 5 stamps, Malvin now has 4/5 as many stamps as Ken. Find the total number of stamps the two boys had at first.

Best wishes

[Brenda10]

tianzhu:

Hi


While waiting for livewith_vanilla to come back with her question, I would like to put up two familiar types of questions concerning two changed quantities. Questions of this genre can be solved using Units and Parts, Model Drawing or Making a list (Equivalent ratio).

You may want to compare them with the question from livewith_vanilla to see the difference.

1)The ratio of Ryan's pocket money to John's pocket money was 3 : 2. After Ryan saved $15 and John spent $8, the ratio of Ryan's pocket money to John's pocket money was 3 : 1. How much money did Ryan have at first?

2) The number of Malvin’s stamps to Ken’s stamps was 2:3. After Malvin bought another 8 stamps and Ken lost 5 stamps, Malvin now has 4/5 as many stamps as Ken. Find the total number of stamps the two boys had at first.

Best wishes

Hi tianzhu

The follwing answer worked out by DD affer learning for the past few days in ratio topics:

Q1: $39
Q2 : Total 150 stamps

Please confirm.

[tianzhu]

Brenda10:

The follwing answer worked out by DD affer learning for the past few days in ratio topics:
Q1: $39
Q2 : Total 150 stamps
Please confirm.

Hi Brenda10

Wow, that was fast.Yes, they are correct.

Best wishes

[Brenda10]

tianzhu:

Brenda10:

The follwing answer worked out by DD affer learning for the past few days in ratio topics:
Q1: $39
Q2 : Total 150 stamps
Please confirm.

Hi Brenda10

Wow, that was fast.Yes, they are correct.

Best wishes

Hi tianzhu

Thank you for your confirmation.

[Vanilla Cake]

tianzhu:

The question posed by livewith_vanilla is an interesting one. Unlike more familiar questions involving two changed quantities, the number (124) involved in the transaction is in one single lot.


Usually questions involving two changed quantities can be solved by Units and Parts, Model Drawing or equivalent ratios where numbers are presented in a tabulated list.

In this particular question, MD is out. If you try to use UP, you’ll also face obstacles. I also hit the dead end trying to get the answer. However, if you try to use equivalent ratios, you’ll be able to get the answer of 26 based on the context in the question.I am not sure if this is the actual question from any test papers or books or just an example given by livewith_vanilla.As such, there may be multiple answers.

CoffeeCat:

Mr tianzhu, is your equivalent ratio method the one where you make two listings of multiples of 13 and 5 separately and pick the first 2 which has a difference of 124?

I agree that this question is too vague ( so multiple solutions existed). Perhaps a sentence should be added saying that only the lowest answer is required.
On the other hand, until livewithvanilla elaborate more, I will think that it is highly unlikely that such a question actually appeared as a homework question for p6. It is my guess that she is trying to illustrate a quick example of questions involving 2 changed quantities.
In any case I look forward to hearing from livewithvanilla the simple method=).

tianzhu:

While waiting for livewith_vanilla to come back with her question, I would like to put up two familiar types of questions concerning two changed quantities types of questions. Questions of this genre can be solved using Units and Parts, Model Drawing or Making a list (Equivalent ratio).

You may want to compare them with the question from livewith_vanilla to see the difference.

Dear Uncle Tianzhu,
My younger sister is concerned about the question posted by \"livewith_vanilla\" as this question is invalid as you will have multiple correct answers. Based on these points from someone who highlighted to my mum in another forum:

1)Initial Amount is a multiple of 13 (6+7) <- List
2)Final Amount is Initial Amount + 124 <- Work this
3)Final Amount is a multiple of 5 (2+3)<- Check this

Solution By List-Work-Check

13, 137, Not multiple of 5 <- rejected
26, 150, OK since multiple of 5

Initial Amount is 26

If the question asked for the lowest answer as mentioned by CoffeeCat, 26 will be the correct answer.Otherwise, multiple answers will exist and confuse readers and other students who will be taking PSLE this year or later on. I have posted my comments in another http://www.kiasuparents.com/kiasu/forum/viewtopic.php?p=192321#192321 in this forum to highlight to \"livewith_vanilla\" to inform us the source of this ambiguous question.
Thanks.

[tianzhu]

Vanilla Cake:

My younger sister is concerned about the question posted by \"livewith_vanilla\" as this question is invalid as you will have multiple correct answers.

Hi VC, let’s wait for the actual question from livewith_vanilla next week.

Her question breaks the usual familiarity of questions involving two changed quantities. You’ll run into stumbling blocks if you try to solve it with Units and Parts and Model Drawing.However, if you use equivalent ratios, you should be able to get an answer of 26 as the numbers involved in the question are small.

Based on the context of the question, 26 is a logical answer. You should not be penalized if you are able to present the solution in a systematic and logical way.

Wait for livewith_vanilla to come back with her original question next week, maybe, PC will learn that her concerns are unfounded.

Forget about this problem for a while and enjoy your weekend.

Best wishes

[tianzhu]

Brenda10:

Hi tianzhu
Thank you for your confirmation.

Hi Brenda10

You're welcome.

Best wishes