Q&A - PSLE Math

[MathIzzzFun]

Jasmy:

Hi,need help on this qn


The ratio of boys to girls who got distinctions in a test is 4:1. This group is 1/4 of the total nos.of pupils. Half as many boys as girls got less than 60%. This is 1/5 of all the pupils. The ratio of boys to girls who scored betw 60% and distinction is 3:2. There are 22 girls in the group. How many boys achieved distinctions?

TIA

Hi

Total number of students --> 100u
Students with distinction --> 1/4 x 100u = 25u
Students scoring less than 60% --> 1/5 x 100u = 20u
Students scoring between 60% & distinction --> 100u - 25u - 20u = 55u
Girls scoring between 60% & distinction --> 2/5 x 55u = 22u
So, 22u --> 22, 1u =1
Number of students with distinction = 25
Number of boys with distinction = 4/5 x 25 = 20

cheers.

[MathIzzzFun]

YumYum:

Hi, can someone pls help with the foll Qns:


1. There are 3 containers A, B and C containing alcohol solution (alcohol and water). The pure alcohol in container A is 48%. The total volume of the alcohol solution in the 3 containers is 100 litres. The volume of the alcohol solution in container A is equal to the total volume of the alcohol solution in container B and C. If we mixed the 3 containers then the alcohol in the mixture is 56%. Find the volume of alcohol in container B and C together.


2. When 2 is subtracted from the denominator of a fraction, the fraction becomes 3/4. If 9 is added to the denominator, the fraction becomes 5/7. Find the original fraction.


thanks!

Hi

Q1 reads more like a word puzzle than a maths question !

Total pure alcohol = 56% x 100L = 56L
Alcohol solution, A = Alcohol solution, B+C = 50L
Pure alcohol, A --> 48% x 50L = 24L
Pure alcohol, B+C = 56L - 24L = 32L

Q2.
Numerator --> 3u
Denominator --> 4u+2

3u : 4u +2+9
= 5 : 7

cross multiply or equalize :
21u = 20u + 55
1u = 55

Numerator = 55 x 3 = 165
Denominator = 55 x 4 + 2 = 222

cheers.

[speedmaths.012624com]

shurley197323:

Hi,pls help. I got 3 qtns from Aitong CA 1paper.


2) X,Y & Z bought a watch for their mum. X paid 1/4 of what Y & Z paid. Y paid 1/5 of what X and Z paid. If Z paid $56 more than Y, how much did the watch cost.
Answer :$120

Thanks in advance.

Hi,

X paid 1/4 of what Y & Z paid.
Let X pay 1 unit, and let Y and Z pay 4 units
Total 5 units.

Y paid 1/5 of what X and Z paid.
Let Y pay 1 unit, and let X and Z pay 5 units
Total 6 units.

Common multiple of 5 and 6 is 30.
Ratio of X:Y:Z is 6u:5u:19u
Total is 6u + 5u + 19u = 30u

Z - Y is 19u - 5u = 14u
14u is $56
1u is $4
30u is 30 x $4 = $120

Answer given as $120 is correct.

Cheers


Speed Maths Centre
http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=43&t=25433&start=10


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[speedmaths.012624com]

BlueBells:

Here's one question. I can't remember the exact wordings, but it goes something like this:


In a hall, if the chairs are arranged 13 in a row, there are 6 in excess. If they are arranged 17 in a row, there are 4 chairs short. If there are between 200 - 300 participants for the event, how many chairs are there?

Thanks for any enlightenment.

Hi,

Based on the wordings given, the answer is a number such that:
If you divide the number by 13, you will get a remainder of 6.
If you divide the number by 17, you will get a remainder of 13 (equivalent to short of 4).

You can make a list of:
a) [(multiples of 13) + 6], e.g. 201, 214, 227, etc.
b) [(multiples of 17) + 13], e.g. 200, 217, 234, etc.

and find a common number.

There is no such number between 200 and 300.
The number 370 is one possible answer.

Cheers



Speed Maths Centre
http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=43&t=25433&start=10



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[YumYum]

Dear MathIzzzFun,


Thank you for your usual help.

[kamom]

Help :please:


http://img.photobucket.com/albums/v606/shirleywoon/SH-Sep2011/MathOlympiadTest1e.jpg\">

THANKS A MILLION

[Winx5015]

Hi,


Below are 2011 PSLE math questions, can anyone help to solve?

(1) Nurul and Peili went shopping together with a total sum of $60. Nurul spent twice as much as Peili. the amount Peili had left was $7 more than what she had spent. She had twice as much money left as Nurul.
(a) How much money did Peili spend?
(b) How much money did Nurul have at first?

(2) Mrs Hoon made some cookies to sell. 3/4 of them were chocolate cookies and the rest were almond cookies. After selling 210 almond cookies and 5/6 of the chocolate cookies, she had 1/5 of the cookies left. How many cookies did Mrs Hoon sell?

Thanks.

[KSP]

Hi Winx5015,


1a. 11, b. 31
2. 960

Is the ans correct?

[bbkoala]

Hi


Need help on the following question:

Mrs Tay bought 72 plastic and wooden hangers. Each plastic hanger costs $1.50 and each wooden hanger costs $3.50. She spent $42 more on wooden hangers than plastic hangers. How many wooden hangers did she buy?

DD’s teacher’s answer is 30.
The steps as follows:
$42/3.50=12, 72-12=60, 60/2=30.

Need help to understand why these steps are taken.

[tianzhu]

Winx5015:

Hi,


Below are 2011 PSLE math questions, can anyone help to solve?

(1) Nurul and Peili went shopping together with a total sum of $60. Nurul spent twice as much as Peili. the amount Peili had left was $7 more than what she had spent. She had twice as much money left as Nurul.
(a) How much money did Peili spend?
(b) How much money did Nurul have at first?

Hi

For Q1,you may use MD.

Start with the “after” MD.

In the end (money left)
Peili ------ 2 units (boxes) + 7
Nurul ------ 1 unit + 3.5

Now work backwards

In the beginning
Peili ------- 2 units + 2 units + 7
Nurul ------- 4units + 1 unit + 3.5

5 units + 7 + 3.5 ------ 60
5 units ------ 49.5
1 unit ------ 5.5

Peili spent ------- (2*5.5) ------- 11

Nurul -------- (5*5.5) + 3.5 ------ 31

Best wishes