Q&A - PSLE Math

[speedmaths.012624com]

kamom:

Help :please:


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

THANKS A MILLION

http://i44.tinypic.com/w8173p.jpg\">

Hi kamom,

The answer is 55 degrees.

Please see diagram.

First, draw a square, say 1 cm by 1 cm.
Next, draw an isosceles triangle on the right, and use trigonometry to find the value of lengths a, b and c.
Then draw another isosceles triangle on the left, and use trigonometry to find the value of lengths d, e and f.

g = c - e

w + x = 70 degrees

tan (w + 70 degrees) = (f + 1 + b) / g

x = (70 degrees - w) = 55 degrees.

The solution I used involves trigonometry, which is normally beyond P6 pupils.

May I know the source of this question?

Cheers


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


.

[thinkgmama]

Thank you do much. I finally understand.

[homeworkmummy]

tianzhu:

homeworkmummy:

Could you pls advise if this can be solved by model method. My DD was confused with the percentage method.

Hi

It’s possible to provide graphical representations of the information in the question.

Perhaps you may want to check with your DD.

What is confusing her?

What is her understanding of percentages after reading her textbooks?

What is her understanding on comparing two quantities of percentages?

Percentages is first started in P5 Maths.Maybe, she is confused because her teacher has not covered the topic in Percentages for her P6 syllabus yet.

Best wishes

Thanks tianzhu. She is not familiar with the comparison method. Is this only cover in p6?

[tianzhu]

homeworkmummy:

Thanks tianzhu. She is not familiar with the comparison method. Is this only cover in p6?

Hi

Good Morning.

You're welcome.

“Finding percentage increase/decrease” is only covered in P6 syllabus.

http://www.moe.gov.sg/education/syllabuses/sciences/files/maths-primary-2007.pdf

Best wishes

[homeworkmummy]

tianzhu:

homeworkmummy:

Thanks tianzhu. She is not familiar with the comparison method. Is this only cover in p6?

Hi

Good Morning.

You're welcome.

“Finding percentage increase/decrease” is only covered in P6 syllabus.

http://www.moe.gov.sg/education/syllabuses/sciences/files/maths-primary-2007.pdf

Best wishes

Thanks Tianzhu for the info.

[tianzhu]

homeworkmummy:

Thanks Tianzhu for the info.

Hi

You’re welcome.

I believe she’ll understand it better when the teacher has covered the topic.

Best wishes

[Chan09]

I do need help as I can solve using algebra but even looking at models this is tough:

a group of friends play tennis. each of them play with everyone else. Ann played with 4 times as many girls as boys. Bob played with 5 times as many girls as boys.
a) how many people were there altogether? ans: 31 people
b) were there more boys than girls and how many more? ans: 19 more girls than boys

[MathIzzzFun]

Chan09:

I do need help as I can solve using algebra but even looking at models this is tough:

a group of friends play tennis. each of them play with everyone else. Ann played with 4 times as many girls as boys. Bob played with 5 times as many girls as boys.
a) how many people were there altogether? ans: 31 people
b) were there more boys than girls and how many more? ans: 19 more girls than boys

Hi

Ann played with 4 times as many girls as boys, so
Girls : Boys --> 4u +1 : 1u,
total 5u + 1 people and there were 3u + 1 more girls

Bob played with 5 times as many girls as boys,
Girls : Boys --> 4u + 1 : 1u -1 = 5 : 1

cross multiply or equalize --> 4u + 1 = 5u -5
1u --> 6
5u + 1 = 31
3u+1 --> 19

There were 31 people and there were 19 more girls than boys.

cheers.

[hazelwong]

Hi, I came across this type of question:

Charlie had $490 more than Eugene. Charlie spent 1/7 of his money, Eugene spent 1/5 of his money. If Eugene spent $20 less than Charlie, find the total amount of money the children had in the end.
The answer given is such a complex model (subdivided into many units) :? that I wonder if there is an easier way?
TIA

[MathIzzzFun]

hazelwong:

Hi, I came across this type of question:

Charlie had $490 more than Eugene. Charlie spent 1/7 of his money, Eugene spent 1/5 of his money. If Eugene spent $20 less than Charlie, find the total amount of money the children had in the end.
The answer given is such a complex model (subdivided into many units) :? that I wonder if there is an easier way?
TIA

Hi

Eugene's money --> 5 units
Eugene spent --> 1 unit
Charlie spent --> 1 unit + 20
Charlie's money --> 7 x (1 unit + 20) = 7 units + 140
So, 7 units + 140 = 5 units + 490
1 unit --> 175
...you should be able to complete the solution from here

cheers.