Q&A - PSLE Math

[tianzhu]

Hi


Questions involving Common Difference.

I wish to add on to my earlier reply to Musicstar’s question on Age Question.

Questions on Common Difference are a regular feature in past years papers. Different term such as Unchanged Difference or Difference Unchanged is also being used.

They can be solved by using MD, UM or UP.Usually, MD is used by the P3/P4 students.

I’ve compiled a list of questions on CD asked by members in KSP forum.
I’ve picked some of them and try to add some pictorials as shown in the slides below.

Generally, they can be grouped as follows:

A) Questions on difference in age.

B) Questions involving two persons receiving an equal amount of money or other objects from another party.

C) Two persons giving away an equal amount of money or other objects to another party.

D) The same number of male/ female spectators leaving a football stadium.

E) Selling/buying an equal number of flowers.

(B) to (E) fall into the same category as transfer to/from two variables.

Football fans imagine, singing Ole, Ole, Ole, in Old Trafford Stadium.

Questions involving Common Difference (KSP).

1) Leon is 45 years older than Peter, in another 2 years times, Leon will be 6 times as old as Peter. How old is Leon now? (52)

2) At present, Ronald is 3 times as old as his sister. In 22 years' time, Ronald's age will be 19 years less than twice his sister's age. How old is Ronald now?(9)

3) The ratio of John's age to his uncle's age is 1:4. In 30 years' time, the ratio will become 2:3. How old is John now? (6)

4) When Mrs. Lee was 40 years old, her son was twice her daughter's age. Mrs Lee will be twice her son's age when her daughter is 28 years old. How old will Mrs Lee be when her daughter is 20 years old? (56 years old)

5) A florist had 84 stalks of orchids and 4 times as many stalks of roses in her shop. After buying an equal number of orchids and roses the ratio of the number of orchids to the number of roses became 5:9.How many stalks of orchids and roses did she buy altogether?( 462)

6) The salary of Mr. Lim and Mr. Tan was in the ratio 3:5. After they gave away an equal amount of $3500 to their wives, the ratio became 1:4. What was Mr. Lim's salary? (4500)

7) A fruit seller had a total of 204 red and green apples in the ratio of 9:8.
After he sold an equal number of each type of apple, the number of red and green apples left was in the ratio of 9:5. How many apples did he sell altogether? (162)

Frank has 2/5 as many blue as red marbles. After buying another 42 blue and 42 red marbles, Frank then had 5/9 as many blue marbles as red marbles. How many marbles did Frank have at first? (168)

9) Father gave Gary $570 and his sister $250. After their mother has
given them an equal amount, Gary’s amount was twice as much as his
sister’s. How much money did their mother give to each of them? (70)

10) Osman had $41 and Mike had $15. After each boy had bought the same textbook each at the bookshop, Osman had 5 times as much money as Mike. How much did the textbook cost? (8.50)

11) In a soccer stadium, the number of female to male spectators is 3:7. After 287 female and 287 male left the stadium, the ratio of female to male spectators became 2:5. How many spectators were there at first? (8610)

12) Dawei has $180 and Yawen has $55. After their aunt gave each of them an equal amount of money, Dawei had twice as much money as Yawen. How much money did their aunt give to each of them? (70)

Best wishes

http://farm9.staticflickr.com/8544/8644901090_8b0038222f_z.jpg\">

http://farm9.staticflickr.com/8099/8643979231_9abe6df1e0_z.jpg\">

[Musicstar]

Hi,


Can someone help to explain the following questions? Although my girl is already P6 but I have been doing this type of questions but still do not understand when to "+" and "-". How do I look at the question to understand? Can someone enlighten me to better understanding? My girl has this question wrong. I think she also still not sure how to do it. Sorry, it may be an easy question for others. Thank you for helping to explain.

Questions: Vicky and her sister have a sum of money . If Vicky gives $120 to her sister, she will have 3 times as much money as her sister. If Vicky gives an additional $40 to her sister, she will have $240 more than her sister . How much money does her sister have?

Answer : 2u = 40 +240+40 = $320
1 u = 160
160 - 120 =40
Her sister has $40.

[Musicstar]

Hi,


Please help . How to get 3 units?


Question: Jack and Jill owned a chicken farm each. If Jack and Jill sold 60 chickens and 30 chickens respectively in a day, Jack would have 300 chickens left when Jill has sold all her chickens. If Jack sold 30 chickens a day and Jill sold 60 chickens a day, Jack would have 930 chickens left when Jill has sold all her chickens. Find the number of chickens Jack has on his farm.

Answer : 3 u = 930 - 300 = 630
1u = 630 / 3 = 210
930 + 210 = 1140
Jack has 1140 chickens on his farm

[MathIzzzFun]

Musicstar:

Hi,


Please help . How to get 3 units?


Question: Jack and Jill owned a chicken farm each. If Jack and Jill sold 60 chickens and 30 chickens respectively in a day, Jack would have 300 chickens left when Jill has sold all her chickens. If Jack sold 30 chickens a day and Jill sold 60 chickens a day, Jack would have 930 chickens left when Jill has sold all her chickens. Find the number of chickens Jack has on his farm.

Answer : 3 u = 930 - 300 = 630
1u = 630 / 3 = 210
930 + 210 = 1140
Jack has 1140 chickens on his farm

similar questions were discussed before ..

A farmer has some chickens and ducks. If he sells 2 chickens and 3 ducks every day, there will be 50 chickens left when all the ducks have been sold. If he sells 3 chcikens and 2 ducks every day, there will be 25 chickens left when all the ducks have been sold.
a) how many ducks are there?
b) how many chickens are there ?
at http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=6410

Vicky and Jane were given a certain amount of money to spend. If Vicky spent $90 and Jane spent $30, Vicky would have $100 left when Jane had spent all her money. If Vicky spent $30 and Jane spent $90, Vicky would have $580 left when Jane had spent all her money, Find the total amount of money given to Vicky and Jane.
at http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=27&t=6373&start=3960

Tammy and Sharon have some money. If Tammy spent $60 each day and Sharon spent $30 each day, Tammy is left with $400 when Sharon spent all her money. If Sharon spent $60 each day and Tammy spent $30 each day, Tammy is left with $1150 when Sharon spent all her money. How much money do the two girls have?
http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=4200

here are 4 possible approaches to tackle such questions:

http://i47.tinypic.com/143n9rb.png\">

http://i49.tinypic.com/w9dtt2.png\">

cheers.

[Musicstar]

HI MathizzzFUn,


Thank you very much for sharing all the method.

MathIzzzFun:

Musicstar:

Hi,

Please help . How to get 3 units?


Question: Jack and Jill owned a chicken farm each. If Jack and Jill sold 60 chickens and 30 chickens respectively in a day, Jack would have 300 chickens left when Jill has sold all her chickens. If Jack sold 30 chickens a day and Jill sold 60 chickens a day, Jack would have 930 chickens left when Jill has sold all her chickens. Find the number of chickens Jack has on his farm.

Answer : 3 u = 930 - 300 = 630
1u = 630 / 3 = 210
930 + 210 = 1140
Jack has 1140 chickens on his farm

similar questions were discussed before ..

A farmer has some chickens and ducks. If he sells 2 chickens and 3 ducks every day, there will be 50 chickens left when all the ducks have been sold. If he sells 3 chcikens and 2 ducks every day, there will be 25 chickens left when all the ducks have been sold.
a) how many ducks are there?
b) how many chickens are there ?
at http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=6410

Vicky and Jane were given a certain amount of money to spend. If Vicky spent $90 and Jane spent $30, Vicky would have $100 left when Jane had spent all her money. If Vicky spent $30 and Jane spent $90, Vicky would have $580 left when Jane had spent all her money, Find the total amount of money given to Vicky and Jane.
at http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=27&t=6373&start=3960

Tammy and Sharon have some money. If Tammy spent $60 each day and Sharon spent $30 each day, Tammy is left with $400 when Sharon spent all her money. If Sharon spent $60 each day and Tammy spent $30 each day, Tammy is left with $1150 when Sharon spent all her money. How much money do the two girls have?
http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=4200

here are 4 possible approaches to tackle such questions:

http://i47.tinypic.com/143n9rb.png\">

http://i49.tinypic.com/w9dtt2.png\">

cheers.

[Oldschool]

Musicstar:

Hi,


Can someone help to explain the following questions? Although my girl is already P6 but I have been doing this type of questions but still do not understand when to \"+\" and \"-\". How do I look at the question to understand? Can someone enlighten me to better understanding? My girl has this question wrong. I think she also still not sure how to do it. Sorry, it may be an easy question for others. Thank you for helping to explain.

Questions: Vicky and her sister have a sum of money . If Vicky gives $120 to her sister, she will have 3 times as much money as her sister. If Vicky gives an additional $40 to her sister, she will have $240 more than her sister . How much money does her sister have?

Answer : 2u = 40 +40+40 = $320
1 u = 160
160 - 120 =40
Her sister has $40.

Hi,

The person who gives will have that sum deducted from his/her share.

Likewise, the person who receives will have that sum added to his/her share.

For a start, it is good to draw table/model and fill it in with the information/clue given.

Perhaps then, it would easier to follow/see and determine what other information is needed to help solve the problem.

Regards

http://www.flickr.com/photos/94858125@N03/8651246076/sizes/c/in/photostream/

[tianzhu]

PapayaDad:

Hi tianzhu,


I learn from your blog too. Thanks a lot.

Hi PapayaDad

So paiseh , actually, the blog was not set up by me because I don’t know how to blog.

You know lah, old man already, only know of “blocks’ in life, not “blogs”

It was Chief who helped to transfer the post from the P5 thread to the blog.

Best wishes

[Easy-going]

Hi

Please help me with this question. Thank you very much in advance.
Question 14 (Rosyth CA 1 2012 Paper Two)
Jack, Meili and Raj shared some 50-cent coins.
They each had an average of 28 coins.
The total amount of money that Jack and Meili had was $7 more than the total amount of Jack and Raj had.
If Raj’s amount was 4 times of Jack’s amount, how much more money did Meili have than Jack?

[PapayaDad]

Cannot get round number leh…

My method:
Average = 28 coins
Total = 28 x 3 = 84 coins = $42

J+M=J+R+7 so M=R+7
R=4J

J=u
R=4u
M=4u+7
Total = 9u+7 = 42
u=3.8888?

[Chalupa]

(I need help for this question !) Mr. Lee left town at 6.45am and drove at a uniform speed of 60km/h to Town Q.Mrs Chen left town P at 7:15am and drove towards Town Q along the same expressway as Mr Lee.She passed him at 10:15am and continued driving at the same speed until she reached Town Q.The distance between Town P to Town Q was 560km.How far was Mr Lee from Town Q when Mrs Chen reached Town Q ?

Thanks in advance.