Q&A - PSLE Math

[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 !

[tianzhu]

Hi elkniwt


This question touches on simultaneous concept.

You may solve it pictorially, using letters of the alphabet or units and parts. There are some examples in some of the earlier posts.

For this question, I’ve chosen 125%:100% as 25:20 so as to make the calculations neater.(5P ----- 20, so you'll get a whole number for P instead of decimals.)

Hope this helps.

Best wishes

http://farm8.staticflickr.com/7161/6707675849_d6e9dec552_z.jpg\">

[sleepyqueen]

PiggyLalala:

MathIzzzFun:

Hi

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

cheers.

Hi MathizzFun,
Can explain how do we know we have to let C to be 75 units?
Thank you very much

Should be \"How to get C to be 60 units\" as presented in the solution
A+B = 125% if C = 75 units. But there is no C = 60 units mentioned in the question.

[MathIzzzFun]

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

u r welcome

cheers.

[MathIzzzFun]

PiggyLalala:

MathIzzzFun:

[quote=\"elkniwt\"]
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.

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

given Area A + Area B = 125% of Area C
so Area A + Area B : Area C = 5 : 4

We can use 5 units for area A + area B and 4 units for area C but we will need to deal with fractions/decimals. Since 1/5 of C was shaded, I decided on a multiple of 20 which is 60 units, but if one is comfortable dealing with decimals, then you can just set area C = 20 units.

cheers.