Q&A - PSLE Math

[ozora]

tianzhu:

Hi


In this question, a student should note that the number of apples and oranges remains the same in both scenarios.

A student who is familiar with SE could proceed to use it. If not, he/she could solve it using the alphabet method or pictorially.

In this illustration, I’ve done it pictorially. As usual, I’ve put in more details than necessary because I wanted to show the flow of events. Once you understand the concept, you may express the solution in your own way.

Best wishes.

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thanks for the help/.. it really makes me understand better to assist my nephews .thanks again

[ozora]

sorry need guide about these questions.

a)The number of 20cents coins to $1 coins in Jane’s box is 5:4. She took out 8 $1 coins and exchanged them into 20 cents coins of the same value. The ratio of the number of 20cents coins to $1 coins became 15: 4. What was the amount of money Jane has?
I used equivalent ratio and got $35. I wondered is the answer correct.

Is it possible to use model or units method? If yes, how?

b) Shop A has 164 more customers than shop B . After 1/4 of the customers in shop A and went to shop B, there was 48 more customers in shop A than in shop A. How many customers were there in shop A and shop B respectively?

[tianzhu]

pixiedust:

Thank you tianzhu. I pay you to tutor my son, can ? :lol:

Hi

Good Morning.

You're welcome.

Thank you for having confidence in me.

Best wishes

[tianzhu]

ozora:

thanks for the help/.. it really makes me understand better to assist my nephews .thanks again

Hi

Good Morning.

You're welcome.

Best wishes

[tianzhu]

Hi


For Q1,you may use Systematic Listing by working out a list of equivalent ratios.
You may also use the concept of “Two changed quantities”

In this illustration, I am using UM, basing on the concept that the total value of coins remains the same before and after.

As for Q2, please refer to the underlined sentence, you may wish to check your source again.

Shop A has 164 more customers than shop B . After 1/4 of the customers in shop A and went to shop B, there was 48 more customers in shop A than in shop A. How many customers were there in shop A and shop B respectively?

I think there are are some missing words in this sentence.Also,it should read as “there were 48 more customers in shop A than in shop B”. The question is also a bit vague, does the number of customers refer to the before or after scenarios. I’ve worked out both.

May I take this opportunity to wish all mothers in KSP a very “Happy Mother’s Day”
And to the two very wonderful women in my life, Thank you for all your support.

Best wishes

http://farm4.static.flickr.com/3452/5694122509_6194739b94_z.jpg\">

http://farm4.static.flickr.com/3281/5694695728_6ab3d5b56a_z.jpg\">

[bobsg01]

To: Tianzhu


:thankyou:

[tisha]

tianzhu:

In this question, you’ll see that the ratios are comparing the quantity or number of notes and not the value of notes. Angel exchanged 12 pieces of $100 into some $5 notes. Hence, the number of notes in the before and after scenarios is different.


Some students may recognise that the value or amount of money remains the same and may prefer to work using the concept of unchanged total quantities.

There are a few ways to solve this question, Units Method, MD or Systematic listing.

Hope this helps

Best wishes

http://farm6.static.flickr.com/5019/5444329416_183f66d5eb_b.jpg\">

Hi Tianzhu or any other sifus,
My DS has solved this Q in the following way. He gets a different ans. Even as I agree to how you have solved, I'm not sure where he has gone wrong? Could you please have a look at his solution and point out where is the mistake?

Before:
$100:$5
7:4
x2
14:8


After:
$100:$5
1:16
x2
2:32

14u-2u = 12u

12u = 12
1u->1

14x100 = 1400
8x5 = 40

1400+40 = 1440

[tianzhu]

Hi tisha


In this question, you’ll see that the ratios given in the question are comparing the quantity or number of notes and not the value of notes.

Angel exchanged 12 pieces of $100 into some $5 notes.12 pieces of $100 with a value of $1200 are changed to 240 pieces of $5 notes. Hence, the number of notes in the before and after scenarios is different.

Some students may recognise that the value or amount of money remains the same and may prefer to work using the concept of unchanged total quantities.

If you choose to rely on the concept that the value of notes remains the same before and after, you’ve have to convert the ratios showing the number of notes into ratios showing value.

There are a few ways to solve this question, Units Method, MD or Systematic listing.

I’ve extracted the solution from one of the earlier posts.

Hope this helps.

http://farm5.static.flickr.com/4149/5446722398_7a9141f966_b.jpg\">

[tianzhu]

tisha:

Could you please have a look at his solution and point out where is the mistake?

Before:
$100:$5
7:4
x2
14:8


After:
$100:$5
1:16
x2
2:32

14u-2u = 12u

12u = 12
1u->1

14x100 = 1400
8x5 = 40

1400+40 = 1440

Hi

Perhaps, you may ask your kid the following questions.

a)12 pieces of $100 notes add up to $1200
They can be changed to 240 pieces of $5 notes
Why did he use 12, what happens to the 240 pieces of $5
notes?

b)Why did he multiply the ratios by 2?

c)Does the number of notes remain the same or change in number before and after?

This’ll help to better understand what went through his young mind when he crafted the solution.

Best wishes


.

[tianzhu]

bobsg01:

To: Tianzhu


:thankyou:

Hi

You're welcome.

Best wishes