Q&A - PSLE Math

[tianzhu]

Hi pixiedust


For your first question, there was quite a similar question discussed in one of the earlier posts.Maybe, it'll help.

The solution to your question.

1 unit ------ 1+3/4 ------7/4
4 units -------7/4*4 ------7

1 part -------- 7+3/4 ------- 31/4
4 parts -------- 31

3 parts ------- 23.25
Sally received (23.25 + 0.75) ------- 24

(Note 3/4 is equal to 0.75)

Best wishes

http://farm5.staticflickr.com/4019/4713599224_8f586290c0_z.jpg\">

[tianzhu]

Hi pixiedust


For the second question,

First day
Male participants ------ 100% + 70
Female participants ------ 100%

Second day
Male participants ------ 80% + 56 (decreased by 20%)
Female participants ------ 110% (increased by 10%)

190% + 56 ------ 531
190% ------ 475
100% ------- 475/190 * 100 ------- 250

Number of participants for first day -------- 250 + 70 + 250 ------ 570
Number of participants for second day -------- 256 + 275 ------ 531

Total number of participants ------ 570 + 530 ------ 1101

Amount collected ------ 1101*35 ------ 38535


For the third question, you may use “Units and Parts”.If you have a copy of Challenging Maths Problems Made Easy by Ammiel Wan, please refer to the chapter on \"Changed Quantities Concept\".

At first
Jane ------- 135
Iris ------- 120

Jane gave away 1 unit (25%).
Iris gave away 4 units.

In the end
Jane ------- 2 parts
Iris ------- 1 part.

Equalise the parts so as to make comparison.

135 – 1 unit -------- 240 – 8 units
7 units ------- 105
1 unit ------- 15

Iris gave away (4*15) or 60 sweets.

Jane had (135 – 15) or 120 sweets in the end.

Best wishes

[pixiedust]

Thank you tianzhu, you saved my life ! Got them all…and will work hard to brush up my revision. Your help much appreciated !

[elkniwt]

Hi MathIzzzFun,

Wow! Thank you for the model method. It's ingenious!! hmm... wonder if my dd can digest it or not. I'll try to explain to her.

Hi sleepyqueen,
My method is similar to yours. I am a bit hesitant to teach my dd simultaneous equations. Are they allowed to use this method?

Thanks everyone!

[Bunny27]

Hi, needs help with these 2 questions?? thanks!!


1.Samuel is 1/4 as old as Meihui. In 5 year’s time, Samuel will be 1/3 as old as Meihui. How old is Meihui now?

2.Steven read an equal number of pages from a storybook each day. After 12 days, he had 4/5 of the pages left. After another 10 days, he had 570 pages left. How many pages were there in the storybook??

TIA！

[Bunny27]

elkniwt:

Hi MathIzzzFun,

Wow! Thank you for the model method. It's ingenious!! hmm... wonder if my dd can digest it or not. I'll try to explain to her.

Hi sleepyqueen,
My method is similar to yours. I am a bit hesitant to teach my dd simultaneous equations. Are they allowed to use this method?

Thanks everyone!

Hi,
Can someone help in these 2 questions:

1.Steven read an equal number of pages from a storybook each day. After 12 days, he had 4/5 of the pages left. After another 10 days, he had 570 pages left. How many pages were there in the storybook?

2. Samuel is 1/4 as old as Meihui. In 5 year's time, Samuel will be 1/3 as old as Meihui. How old is Meihui now?

TIA

[KSgal]

Hi,


1.
Now:
S : M Diff
1u : 4u 3u

5 yrs time:
S : M Diff
1u 3u 2u

The concept here is constant difference since the age difference between Samuel and Meihui will always be the same. So, we make the difference the same for both ratios, whether it is now or 5 yrs later.

Now:
S : M Diff
2u : 8u 6u

5 yrs time:
S : M Diff
3u : 9u 6u

The difference between the no. of units of now and 5 yrs time is 1u. Thus, 1u–5 yrs
Meihui now has 8units. So, 8x5yrs=40yrs
Meihui is now 40yrs old.

[PiggyLalala]

MathIzzzFun:

elkniwt:

[quote=\"jesschan\"]And does anyone have the complete question to Q18 of paper 2? The total area of triangles A & B is missing in my copy.


Many thanks!

Dear jesschan,

It is also blank on my copy. But I think it is 125% (my guess), cos I could get the answer 3/22 using this value.

Here's the question. I put in 125% in red (only my guess).
http://i44.tinypic.com/1zr1jq9.jpg\">

Dear tianzhu and MathIzzzFun,
I only know how to do this question using simultaneous equations. :oops: Could you please help to advise how to do this question in suitable method. Thank you very much.

Hi

http://www.flickr.com/photos/62167097@N02/6705370185/in/photostream

cheers.[/quote]Hi MathizzFun,
Can explain how do we know we have to let C to be 75 units?
Thank you very much

[KSgal]

2. 12 days–read 1/5 of book

10 days–1/5/12x10=1/5x1/12x10=1/6 of book
22 days–1/6+1/5=11/30 of book
19/30 of book not read–570
1/30 of book–570/19=30
30/30 of book–30x30=900

Ans:900 pages

Hope this helps! ^_^

[Bunny27]

KSgal:

2. 12 days--read 1/5 of book

10 days--1/5/12x10=1/5x1/12x10=1/6 of book
22 days--1/6+1/5=11/30 of book
19/30 of book not read--570
1/30 of book--570/19=30
30/30 of book--30x30=900

Ans:900 pages

Hope this helps! ^_^

Thank you for your assistance !