Q&A - PSLE Math

[tianzhu]

PuzzledboutTHISandTHAT:

There are two bags of stones labelled A and B. In Bag A, there are 350 black stones and 500 white stones. In Bag B, there are 400 black stones and 100 white stones. How many black and white stones should be transferred from bag B to bag A so that 50%of the stonesin bagA and 75%of those in bagB are black? :Can you do the model method?Thks...

Hi

Your question is similar to one of the earlier posts in this thread.

This question has two unknowns and one is required to use simultaneously equation(SE) to solve it. If a student is comfortable with SE, he/she may use it.

I’ll share how to solve SE with visual representation.

The numbers in the earlier question are different but you should be able to solve your question with the same strategy.

Best wishes.

http://farm5.static.flickr.com/4122/4778205021_8f7608186f_b.jpg\">

[octopusmum]

Hi kancheongmum and tianzhu

Tks for your help, hope there won’t be such questions in psle next week!

[tianzhu]

octopusmum:

Hi kancheongmum and tianzhu

Tks for your help, hope there won't be such questions in psle next week!

Hi

You're welcome.

Best wishes

[abc_parent]

hey Vanilla Cake

all the best for your exams too!

[tianzhu]

Hi


Ali,Bala and charles shared a tin of cookies. Ali took 5/6 of the tin of cookies and 1/3 of a cookie. Bala took 5/6 of the remaining tin of cookies and 1/3 of a cookie. Charles received only 2 cookies. How many more cookies did Ali have than Bala?

Q17 from Rosyth CA1 2009, the answer given in the WS is 60.
Please help to confirm if it is correct.

Best wishes

[Vanilla Cake]

tianzhu:

Hi


Ali,Bala and charles shared a tin of cookies. Ali took 5/6 of the tin of cookies and 1/3 of a cookie. Bala took 5/6 of the remaining tin of cookies and 1/3 of a cookie. Charles received only 2 cookies. How many more cookies did Ali have than Bala?

Q17 from Rosyth CA1 2009, the answer given in the WS is 60.
Please help to confirm if it is correct.

Best wishes

Hi Tianzhu,

This question was first posted by http://www.kiasuparents.com/kiasu/forum/viewtopic.php?t=6373&postdays=0&postorder=asc&start=790 on Mon Apr 12, 2010 8:43 am.
It had been answered by http://www.kiasuparents.com/kiasu/forum/viewtopic.php?t=6373&postdays=0&postorder=asc&start=790 on Mon Apr 12, 2010 9:02 am
and
http://www.postimage.org/image.php?v=gxxlNRS on 12 Apr 2010 13:12

VC's mum

[tianzhu]

Hi VC’s mum


Thank you for your reply.

It really jolted my memory.

What a strange thing to do? I’ve actually answered this question when your daughter requested for it.It’s on pg 138 of this thread.

http://www.kiasuparents.com/kiasu/forum/viewtopic.php?t=280&postdays=0&postorder=asc&start=1370

Well, I’ve to admit I am getting old.

Best wishes

[the kiasu student]

hi all,


My teacher gave us another question again.

At a fitness carnival,1600 people participated in a Mass Dance and Taiji. 30% of the Mass dance participants were adults. 40% of the Taiji participants were children. During a break, some Mass Dance participants went to join Taiji and some Taiji participants went to join the Mass Dance. After the change, 25% of the Mass Dance participants and 75% of the Taiji participants were adults. How many Mass Dance participants were there after the change?


I could not make 1 unit of Taiji & Mass Dance participants the same. Please help! :stupid: :udawoman: :udaman: :clubmyself: :lovesite: :dancing: :boogie:

[iFruit]

the kiasu student:

hi all,


My teacher gave us another question again.

At a fitness carnival,1600 people participated in a Mass Dance and Taiji. 30% of the Mass dance participants were adults. 40% of the Taiji participants were children. During a break, some Mass Dance participants went to join Taiji and some Taiji participants went to join the Mass Dance. After the change, 25% of the Mass Dance participants and 75% of the Taiji participants were adults. How many Mass Dance participants were there after the change?


I could not make 1 unit of Taiji & Mass Dance participants the same. Please help! :stupid: :udawoman: :udaman: :clubmyself: :lovesite: :dancing: :boogie:

Let Participants in Mass Dance = 100M
Participants in Taji = 1600 -100M = 100 (16-M)

BEFORE

Adults in Mass Dance = 30M
Children in Mass Dance = 70M

Adults in Taiji = 60(16 -M)
Children in Taiji = 40(16-M)

AFTER break,

Adults in Mass dance = 30M -5M = (25M)--------> (25%)
Children in Mass Dance =70M+5M = (75M)-------->(75%)

Adults in Taiji = 60(16-M)+15(16-M) = 75(160-M) -----> (75%)
Children in Taiji = 40(16-M)-15(16-M) = 25(16-M) ------> (25%)

Adults lost in Mass Dance = Adults gained in Taiji

5M = 15(16-M)-----> M = 12

After break, Adults in Mass Dance = 30M-5M = 25M = 25x12 = 300

PS: IMHO, The question should state that numbers of taiji/mass dance participants don't change after redistribution.

[tianzhu]

the kiasu student:

hi all,

My teacher gave us another question again.

At a fitness carnival,1600 people participated in a Mass Dance and Taiji. 30% of the Mass dance participants were adults. 40% of the Taiji participants were children. During a break, some Mass Dance participants went to join Taiji and some Taiji participants went to join the Mass Dance. After the change, 25% of the Mass Dance participants and 75% of the Taiji participants were adults. How many Mass Dance participants were there after the change?

Hi the kiasu student

Good Morning.

First, please take a few moments to compare your question with this one, (I think it’s from RGPS).

Container A contains 250 red marbles and 200 blue marbles.
Container B contains 600 red marbles and 150 blue marbles.
How many red and blue marbles must be moved from Container A to Container B such that 25% of the marbles in Container A are red and 75% of the marbles in Container B are red?

This RGPS question has two unknowns, and one can solve it with Simultaneously Equations(SE).If a student is comfortable with algebraic manipulation, he/she could use SE through substitution or elimination method.Otherwise, he/she may solve it with SE through visual representation using boxes or circles.

I think there is some missing information in your question. The concept is the total number of participants remains the same; you’ve the same number of adults and children in both scenarios.

Now compare your question with this one.

In Hall A, 30% of the 800 people were men. In Hall B, 40% of the 400 people were women and children. After some of the people in both halls had switched hall, 25% of the people in Hall A and 75% of those in Hall B were men.How many people are there in Hall B after the change?

Do you see the differences?There is a cap on the number of adults and the number of children,therefore, you'll get one answer.In your question, there are no limiting numbers, hence, I think you can have many answers.

I suggest you check with your teacher, please come back to share with other kids the solution once you get it.

May you be blessed with a successful PSLE 2010.

Best wishes