Q&A - PSLE Math

[tianzhu]

ozora:

2.when mrs Toh was 40 years old, her son was twice her daughter's age. Mrs Toh would be twice her son's age when her daughter is 28 years old. How old will mrs Toh be when her daughter was 20 years old?

Hi

A similar question was discussed earlier.

Best wishes.

http://farm3.static.flickr.com/2608/3970452550_9e426aa382_z.jpg?zz=1\">

[tianzhu]

ozora:

1. Don walked from home to school. He was walking at an ave speed of 35m/min for the 1st 5min. He increased his speed by 10m/min when he realized he was going to be late for 4 mins. As a result, he was early by 2 mins. What is the distance bet the school n home?

Hi

Draw a timeline to show the relationships.

Speed ratio ------35:45 ------ 7:9
Time ratio -------9:7

9-7 -----2

2 units ------ 2+4 ------6 min
1 unit ------3 min

7 units ------21

21*45 ------945

5*35 ------ 175

175+945 ------1120

Best wishes

[PiggyLalala]

tianzhu:

ozora:

1. Don walked from home to school. He was walking at an ave speed of 35m/min for the 1st 5min. He increased his speed by 10m/min when he realized he was going to be late for 4 mins. As a result, he was early by 2 mins. What is the distance bet the school n home?

Hi

Draw a timeline to show the relationships.

Speed ratio ------35:45 ------ 7:9
Time ratio -------9:7

9-7 -----2

2 units ------ 2+4 ------6 min
1 unit ------3 min

7 units ------21

21*45 ------945

5*35 ------ 175

175+945 ------1120

Best wishes

Hi tianzhu,
Though my child is not sitting for PSLE this year, I have been reading your solution. I am very touched by the effort and the time you spent in helping to answer the questions almost immediately after the questions have been posted. (Especially so after knowing that you are not a tutor )

Just want to say A BIG THANK YOU to you. :thankyou:

[tianzhu]

Hi


NY SA2 Q17 2010

It helps to draw a simple diagram.

Scenario 1
At first
Blue --- 3 units + 70
White --- 4 units

Scenario 2
At first
Blue --- 8 parts
White --- 7 parts + 112

8 parts ------ 3 units + 70
7 parts ------4 units -112

Equalise the parts

56 parts ------ 21 units + 490
56 parts ------ 32 units – 896
1 unit ----- 126

Blue marble at first ------ 448 (3 units + 70)
White marbles at first ------ 504 (4 units)

After adding 48 more blue marbles
448+48 ----- 496
Total marbles ------ 496+504 ------1000

496/1000*100 ------49.6%

Best wishes

[ozora]

Thanks tianzhu.

[tianzhu]

ozora:

3.I have some almond n butter cookies. If she packs 1 almond n 1 butter cookie, there will be 60 butter cookies left. If she packs2 almond with 3 butter, there will be 50almond cookies left. How many cookies r there in all?

Hi

You may use MD to solve it. I’ll give you some pointers.

Draw 2 big boxes. Add 60 butter cookies. For illustration purposes here, let’s call 1 box “1 part”

Draw two smaller boxes to show almond cookies. Add 50 to them. Next add 3 identical boxes to show butter cookies. Let’s name each small box “1 unit”

The number of cookies in both scenarios is the same.

1 part ----- 2 units + 50

Compare butter cookies
2 units + 50 + 60 ------ 3 units
1 unit ----- 110

Number of cookies ------ 5 units + 50 ------ 600

Best wishes

[Daddy]

Hi,

Need help.

1. Gina spent $270 on a CD player and 2/9 of the remainder of her money on a handbag. Then, she bought blouse for $60. If she had 1/9 of her money left, how much did she have at first?

2. Raphael had $40 less than Sam. When he spent 1/8 of his money and Sam spent 3/4 of his money, Raphael had $80 more than Sam. How much money did Sam have left.


Thanks

[MathIzzzFun]

Daddy:

Hi,

Need help.

1. Gina spent $270 on a CD player and 2/9 of the remainder of her money on a handbag. Then, she bought blouse for $60. If she had 1/9 of her money left, how much did she have at first?

2. Raphael had $40 less than Sam. When he spent 1/8 of his money and Sam spent 3/4 of his money, Raphael had $80 more than Sam. How much money did Sam have left.


Thanks

Hi

http://i52.tinypic.com/2i11tgy.jpg\">


http://i51.tinypic.com/23mx1f5.jpg\">

cheers.

[tianzhu]

Hi


CHS SA2 Q18 2010
\t
This question touches on two concepts

(a) ------ Constant Difference or Unchanged Difference
(b) ------ Changed Quantities

I don’t have time to prepare slides. Please try to consolidate the solutions in tabulated form as it’ll be neater.

Speakers
Male ------ 8
Female ------ 5
Difference -------3

Participants
Male ------ 1 ------ 10
Female ------1 ------ 10

Total number
Male ------- 6 --------18
Female ------ 5 -------15
Difference -------1 ------ 3

For part (a)

Students should note that this is a ratio question involving “Constant Difference” or “Unchanged Difference”.

The difference between the male and female speakers and the difference between men and women (speakers + participants) in the conference are the same.

Total number ------ 33 units
33- 13 ------ 20

20 units are to be divided equally between male and female participants.

Ratio of male speakers to male participants -------8:10 ------4:5

For part (b), the question involves “Changed Quantities concept”. Here, the quantities at the beginning and the end are different.

At first

Participants
Male ------ 10 units - 40
Female -----10 units + 60

In the end
Male ------ 3 parts
Female -----4 parts

Equalise the parts or cross multiply.

40 units -160 ------30 units +180
10 units ------ 340
1 unit ------34

Number of speakers ------13*34 ------ 442

Best wishes

[tianzhu]

Hi


CHS SA2 Q17 2010

I prefer to change percentages into units first before proceeding further with the solution.

Daniel ------140% ------- 7 ------ 35
Brandon ------ 100% ------ 5 ------ 25

Daniel and Brandon each give 20% of their share to Calvin
Daniel ------ 7
Brandon ------ 5

Calvin receives 12units from Daniel and Brandon
12 units ------ 80%
15 units ------ 100%

In the end, Calvin had 27 units and Daniel had 28 units.

28-27 ------1
1 unit ------20

At first, Brandon had (25*2) or 500 stickers.

Best wishes