Q&A - PSLE Math

[MathIzzzFun]

ozora:

i need help on this question.

thanks http://i53.tinypic.com/al3jb4.jpg\">

Hi

http://i54.tinypic.com/2d2jnt.jpg\">

cheers.

[tianzhu]

ozora:

may i know how to i trace back a solution to the following solution?

Jane and Grace shared a sum of money. If jane gave 1/4 of her share to Grace, Grace would have $400 more than Jane. If Jane gave 1/5 of her share to Grace,
Grace would have $154 more than Jane. How much money did they have altogther?

Hi

This is not an easy question, especially under examination conditions for kids.

It’s helpful to see that this question touches on the “double if” scenarios.

The word “if” signals that the scenario did not really happen.It is applicable to only that particular condition.

You may use MD or UM.

I’ll use UM because “not much time”. Actually it may be easier to use UM for this question.

The key point is to see that the total amount of money Jane and Grace had remains the same in the two scenarios.

Scenario 1
If Jane gave 1/4 of her share to Grace, Grace would have $400 more than Jane.

Use 20 units as the common multiple. (4 and 5)

Jane ----- 15 units
Grace ------ 15 units + 400

Total ------- 30 units + 400

Scenario 2
If Jane gave 1/5 of her share to Grace,Grace would have $154 more than Jane.

Jane ----- 16 units
Grace ------ 16 units + 154

Total ------- 32 units + 154

32 units + 154 ------- 30 units + 400

1 unit ------ 123

(30*123) + 400 ------ 4090

They have $4090.

Best wishes

[ozora]

tianzhu:

ozora:

may i know how to i trace back a solution to the following solution?

Jane and Grace shared a sum of money. If jane gave 1/4 of her share to Grace, Grace would have $400 more than Jane. If Jane gave 1/5 of her share to Grace,
Grace would have $154 more than Jane. How much money did they have altogther?

Hi

This is not an easy question, especially under examination conditions for kids.

It’s helpful to see that this question touches on the “double if” scenarios.

The word “if” signals that the scenario did not really happen.It is applicable to only that particular condition.

You may use MD or UM.

I’ll use UM because “not much time”. Actually it may be easier to use UM for this question.

The key point is to see that the total amount of money Jane and Grace had remains the same in the two scenarios.

Scenario 1
If Jane gave 1/4 of her share to Grace, Grace would have $400 more than Jane.

Use 20 units as the common multiple. (4 and 5)

Jane ----- 15 units
Grace ------ 15 units + 400

Total ------- 30 units + 400

Scenario 2
If Jane gave 1/5 of her share to Grace,Grace would have $154 more than Jane.

Jane ----- 16 units
Grace ------ 16 units + 154

Total ------- 32 units + 154

32 units + 154 ------- 30 units + 400

1 unit ------ 123

(30*123) + 400 ------ 4090

They have $4090.

Best wishes

thanks.. i can see clearly on this.

now i tried it on the this following question: but i got stuck. can U see where i go wrong?
Ashley and Bee shared a sum of money. If Ashely spend $10 each day and Bee spend $20 each day, Ashely would have $250 left while Bee would have spend all her money. If Ashely spend $20 each day and Bee spend $10 each day, Ashely would have $10 left while Bee would have spend all her money. How much money did they have resepctively?

Case 1:
A -1 unit +250
B- 2 units
Assuming 1 unit - $10

case 2:
A- 3 unit +10
B- 2 units

2 units= 250-10 =240
1unit -120
a- 360
the answer is wrong.

[ozora]

MathIzzzFun:

ozora:

i need help on this question.

thanks http://i53.tinypic.com/al3jb4.jpg\">

Hi

http://i54.tinypic.com/2d2jnt.jpg\">

cheers.

thanks for the alternative solution

[ozora]

tianzhu:

ozora:

i need help on this question.

thanks http://i53.tinypic.com/al3jb4.jpg\">

Hi

Good Morning.

There are a few ways to solve it.You may use equivalent ratios by assigning units, UM or MD.

The numbers in your question are pretty small. Actually in this case, it’s not too tedious to assign units and work systematically to the answer.

Assign 1 unit to the shaded part. Assign 1 unit to the unshaded area of the small square.

Hence, area of big square is 4 units and area of unshaded area of big square is 3 units.This satisfies all the conditions in your question.

1 unit ----- 20
2 units -----40

Area of small square ----- 40 sqcm

Next, I’ll share the UM method.

This is a question on “Common Difference” or “Unchanged Difference”. I believe you’ve used them in answering questions on the topic “Ratio”.

The difference in areas between the two squares and the difference in unshaded areas between the two squares are equal.

Area of small square ----- 1 unit
Area of big square ----- 2 units
Difference -------1 unit

Area of unshaded part of small square ------- 1 unit
Area of unshaded part of big square ------- 3 unit
Difference -------2 units

Make the difference the same

Area of small square ----- 1 unit ----------2units
Area of big square ----- 2 units --------4 units
Difference -------2 unit

1 unit ------20
2 units -------40

Area of small square ----- 40 sqcm

Best wishes

thanks.. :imcool:

[ck123]

Hi all


I am having problem uploading the pictures for RGS 2011 Prelim Paper 1 Q27 and Paper 2 Q17. Anyone have the solutions? Please help.

Thanks

[tianzhu]

ozora:

now i tried it on the this following question: but i got stuck. can U see where i go wrong?
Ashley and Bee shared a sum of money. If Ashely spend $10 each day and Bee spend $20 each day, Ashely would have $250 left while Bee would have spend all her money. If Ashely spend $20 each day and Bee spend $10 each day, Ashely would have $10 left while Bee would have spend all her money. How much money did they have resepctively?

Case 1:
A -1 unit +250
B- 2 units
Assuming 1 unit - $10

case 2:
A- 3 unit +10
B- 2 units

2 units= 250-10 =240
1unit -120
a- 360
the answer is wrong.

Hi

There is an error as highlighted. It should be read as 4 units + 10

1 unit ---- 80

Ashley ----- 330
Bee ----- 160

Best wishes

[Daddy]

Thanks alot MathIzzzFun.

:thankyou:

[Vanilla Cake]

ck123:

I am having problem uploading the pictures for RGS 2011 Prelim Paper 1 Q27 and Paper 2 Q17. Anyone have the solutions? Please help.

http://i53.tinypic.com/15cy9k.png\">
Answer given: 91.4 cm

http://i51.tinypic.com/x1n6zl.png\">
Answer given: (a) 138.06 cm2 (b) ~83.91 cm

Pls wait for Uncle tianzhu / MathIzzzFun to provide worked solutions.
Thks.

[ck123]

:thankyou: vanilla cake


How did you manage to attach the picture?