Q&A - PSLE Math

[MathIzzzFun]

thisis2012:

MathIzzzFun:

[quote=\"zeepo\"]

Hi, I am new to this forum. Would appreciate if someone could help me with the followings:


2) Anna and Ben take 9 days to complete a jigsaw puzzle. Ben and Celine take 3 days to complete the same jigsaw puzzle. When Celine partners with Dennis, they take 4 days to complete the jigsaw puzzle. How many days will Anna and Dennis take to complete 2 such jigsaw puzzles?

Thanks.

http://tinyurl.com/mathizzzfun-workrate03

cheers.

why total amount of work -> 36 units?
thanks[/quote]lowest common multiple of 9,3 & 4 = 36

Alternatively, you can also work in fractions ..

in 1 day,
A + B --> 1/9 puzzle
B + C --> 1/3 puzzle
C + D --> 1/4 puzzle

A +D --> (1/9+1/3+1/4 - 2 x 1/3) puzzle = 1/36 puzzle

To complete 2 puzzles, A + D will take --> 2 ÷ 1/36 = 72 days

cheers.

[cimman]

zeepo:

3) In a car park, there are thrice as many cars as vans. The number of cars is twice the number of motorcycles. The total number of wheels these vehicles have is 4598.

a) How many cars are parked at the car park?
b) If 1/3 of the motorcycles left the car park, how many vehicles are left in the car park?

here's 2 methods for your child. In the first method, it uses traditional simultaneous equations. In the 2nd method, the u and p are made the same, this essentially eliminates one unknown early on in the process and thus leads to a simpler equation. However, both uses the same equations.

First, we transfer the values directly to the table:
http://i46.tinypic.com/2znwn6g.png\">

Method 1: then we fill up the blank boxes [red fonts] and circle the equations:
http://i48.tinypic.com/mlcoh.png\">

Method 2: here we process the middle row values first, by making u and p the same, which is the conventional approach. Why do we do this ? because this eliminates one unknown variable from a 2 unknown variable equation. Compare this to method 1 and you'll see how the 2 equations are derived.
The table gives a graphical view of all the relationships in the problem sum. All unit value questions or (number x group) questions can be represented in this table.
http://i49.tinypic.com/wsntle.png\">

[Beikiasu]

Hi, can someone help me to solve this problem sum? SCG, 2011,

SA 1, Question 18, 5 mark. Answer $105. Thanks.

Gina, Mary and Alyssa have some money. They want to buy a handbag for their mother. Gina has $30 more than Mary.

If Gina buys the handbag, the ratio of her money left to that of Mary and Alyssa is 9:24:27 respectively.
If Mary buys the same handbag, the ratio of her money left to that of Gina and Alyssa is 1:10:9 respectively.
If Alyssa buys the same handbag, the ratio of her money left to that of Gina and Mary is 1:5:4 respectively.
What is the cost of the handbag?

[MathIzzzFun]

Beikiasu:

Hi, can someone help me to solve this problem sum? SCG, 2011,

SA 1, Question 18, 5 mark. Answer $105. Thanks.

Gina, Mary and Alyssa have some money. They want to buy a handbag for their mother. Gina has $30 more than Mary.

If Gina buys the handbag, the ratio of her money left to that of Mary and Alyssa is 9:24:27 respectively.
If Mary buys the same handbag, the ratio of her money left to that of Gina and Alyssa is 1:10:9 respectively.
If Alyssa buys the same handbag, the ratio of her money left to that of Gina and Mary is 1:5:4 respectively.
What is the cost of the handbag?

discussed on pg 573-
http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=5720

cheers.

[Beikiasu]

Thanks Mathlzfun! :thankyou:


May I know where the cost of handbag --21u come from?

[MathIzzzFun]

Beikiasu:

Thanks Mathlzfun! :thankyou:


May I know where the cost of handbag --21u come from?

total amount left will be the same in case.

depending on which person buys the bag, the amount left by that person will be reduced by the number units equal to cost of handbag

gina has 30u, if she buys handbag, she is left with 9u, handbag--> 21u

alyssa has 27u, if she buys handbag, she is left with 6u, handbag --> 21u

mary has 24u, if she buys handbag, she is left with 3u, handbag --> 21u

cheers.

[Beikiasu]

Mathlzzfun :thankyou: :thankyou:

[Beikiasu]

Hi, can someone help me to solve these problem sum?

1) Joycee has some $2, $5 and $10 notes.The number of $2 notes is 25% of the total number of notes.The ratio of $5 notes to the total number of$2 and $10 notes is 2:5. Given that there are 18 more $10 notes than $2 notes, how much money does
Joycee have in all? CHIJ, 2011, Question 17, 5 mark, Answer $552.

2) 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? CHIIJ, 2011, Qusetion 9, 3 mark, Answer 462. Thanks.

[Beikiasu]

Hi, can someone help me to solve these problem sum?

1) Joycee has some $2, $5 and $10 notes.The number of $2 notes is 25% of the total number of notes.The ratio of $5 notes to the total number of$2 and $10 notes is 2:5. Given that there are 18 more $10 notes than $2 notes, how much money does
Joycee have in all? CHIJ, 2011, Question 17, 5 mark, Answer $552.

2) 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? CHIIJ, 2011, Qusetion 9, 3 mark, Answer 462. Thanks.

[Oldschool]

Beikiasu:

Hi, can someone help me to solve these problem sum?

1) Joycee has some $2, $5 and $10 notes.The number of $2 notes is 25% of the total number of notes.The ratio of $5 notes to the total number of$2 and $10 notes is 2:5. Given that there are 18 more $10 notes than $2 notes, how much money does
Joycee have in all? CHIJ, 2011, Question 17, 5 mark, Answer $552.


A.

No. of $2 is 25% or ¼ of the total number of notes.
Ratio of no. of $2 : total no. of notes = 1:4
Or,
Ratio of no. of $2 : no. of $5 and $10
= 1 : 3
Ratio of no. of $5 : no. of $2 and $ 10
= 2 : 5

B. Both ratio have the same total no. of notes. So,

$2 : $5 + $10
= 1 : 3
= 7: 21 (total = 28)

And,

$5 : $2 + $10
= 2 : 5
= 8 : 20 (total = 28)

C. Then,

Ratio of no. of $2 : no. of $5 : no. of $10
= 7 : 8 : 13
= 7U : 8U : 13U

13U -7U = 18
U = 3

So,
Ratio of no. of $2 : no. of $5 : no. of $10
= 21 : 24 : 39

D. Total $ = 21x$2 + 24x$5 + 39x$10 = $552


2) 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? CHIIJ, 2011, Qusetion 9, 3 mark, Answer 462. Thanks.

A. Before,

Ratio of orchids : roses
= 84 : 4x84
= 84 : 336

B. After,
Ratio of orchids : roses
= 84 + U : 336 + U
= 5 : 9

(84 + U) 9 = (336 + U)5
U = 231

C. 2U = 2x231 = 462

Regards