Q&A - PSLE Math

[tianzhu]

Hi


Hope this helps.
Best wishes

http://farm5.static.flickr.com/4127/4982279423_aee19502f7_b.jpg\">

[James Ang]

You can follow tianzhu's diagram which is correct.


To add,

The rate for candle A is 1/5 per hour, means 4/20 per hour (4u)
The rate for candle B is 1/4 per hour, means 5/20 per hour (5u)
That's why burning rate is 4:5

Candle A [][][ 4u ] =5h
Candle B [][ 5u. ] = 4h
[] = 1 u, total length is 6u, so

4/6 x 5h = 3 and 1/3 h
Or
5/6 x 4 h = 3 and 1/3 h

underthesea:

James Ang:

The solution supplied with the set of prelims paper is wrong for question 18 and it is solved using algebra, and in one of the step the solution showed 7 instead of 9. The correct answer is Vanilla = 72 and Chocolate = 138 after correcting for that wrong step. question 17 on the two candles is interesting, it is exactly the same as what
I mentioned weeks ago, source is a sec 1 textbook, but can be easily solved by drawing a model. Again the supplied solution uses algebra which p6 students may not be taught to solve using algebra.
[quote=\"Vanilla Cake\"]Susan has some vanilla and chocolate sweets in her bag. If she adds 20 vanilla sweets into the bag, the percentage of vanilla sweets in the bag becomes 40%. If she adds 30 chocolate sweets, there will be 70% of chocolate sweets in the bag. How many vanilla and chocolate sweets does she have? [5 marks][Answer given: 64 vanilla sweets and 126 chocolate sweets]

Thank you for your time and effort. I appreciate your help as I think that the answer given is incorrect.

My answers are : Vanilla sweets: 72 and Chocolate sweets: 138
Took me about 10 min plus using 2 different methods to crack this problem sum.Pls help to clarify if I am correct or the given answer is correct.

Can you provide the solution without using algebra? Many thanks.[/quote]

[BryBenMum]

Vanilla Cake:

BryBenMum:

Ailing, Bala, Chris and Dawn shared the cost of a gift for their friend. Ailing paid 1/5 of the amt paid by Bala, Chris and Dawn. Chris paid 40% of the amt paid by Ailing and Bala. The total amt paid by Ailing and Bala is equal to that paid by Chris and Dawn. Given that Dawn paid $32 more than Ailing for the gift, what was the cost of the gift?

A : B+C+D
1 : 5
5 : 25

A+B : C+D
1 : 1
15 : 15

A: 5u
B: 15u-5u = 10u
C+D: 25u-10u=15u

C paid 40% of A+B -> 40/100x15u=6u
15u-6u=9u

D-A = 9u-5u = 4u

4u-> $32
u -> $8

Cost of gift = 30u = 30x$8 = $240

Thank You !

[tianzhu]

A pair of hamsters can give birth to a pair of baby hamsters every month. Each pair of baby hamsters needs 1 month to mature and then this pair of hamsters will in turn give birth to a pair of baby hamsters every month. How many pairs of hamsters are there after 6 months? (4 marks)

Hi kancheongmum

If you are still interested to find out more about the hamster question, you can look for this book which I saw in Popular.
.
Primary 5/6 Maths Olympiad: Unleash The Maths Olympian In You! (Advanced)

https://www.popular.com.sg/jsp/product/product_detail.jsp?vca001=255&vpd001=82847

Read the topic on Fibonacci Numbers, instead of hamsters, the question is about rabbits and the answer is 233 pairs after one year. I am sorry; this is all I can remember, as my old mind is crowded out by burdens of life.

As there is still time before PSLE, your boy may want to take a look at it.

Best wishes

[kancheongmum]

Hi Tianzhu

Need help in these 2 questions, solutions posted but cannot understand
2010 prelim papers Maha Bodhi Q12 Meals question
2010 prelim papers River Valley Q18 vanilla and chocolate sweets
Thank you

[Vanilla Cake]

kancheongmum:

Hi Tianzhu

Need help in these 2 questions, solutions posted but cannot understand

Sorry for the interruption,have you checked Observer's solutions?

kancheongmum:

2010 prelim papers Maha Bodhi Q12 Meals question

http://psle2010a.blogspot.com/2010/09/decimal-p6-2010-sa2-maha-bodhi-p2-q12.html

kancheongmum:

2010 prelim papers River Valley Q18 vanilla and chocolate sweets

http://psle2010a.blogspot.com/2010/09/rvps-p6-prelim-2010-p2-q18.html

VC's mum

[tianzhu]

kancheongmum:

Hi Tianzhu

Need help in these 2 questions, solutions posted but cannot understand
2010 prelim papers Maha Bodhi Q12 Meals question
2010 prelim papers River Valley Q18 vanilla and chocolate sweets
Thank you

Hi kancheongmum

Please refer to VC's mum's post.

Please let me know if I can be of any help.

Best wishes

[Dharma]

Suz855:

Hi,


Need help on the solution for the following question, thanks

A,B, C and D shared a box of pens. A received 20% of the total number of pens which B, C and D received altogether. B received 50% of the total number of pens which A, C and D received altogether. C received 80% of the total number of pens which A, B and D received altogether. D received 6 pens. How many pens were in the box at first?

Ans : 108
:oops: [/img]

A => 1/6
B => 1/3
C => 4/9
D = 1- 1/6 – 1/3 – 4/9 = 1/18
1/18 => 6 pens
18/18 = 18 x 6 = 108 pens

[tianzhu]

Circle P6 2010 SA2 Nanyang P2 Q18

18. The figure below is created using the curved lines (arcs) of quadrants with radius 1 cm, 2 cm and 3 cm. Find the area of the shaded parts.
(Take pi as 3.14)

Q18 looks intimidating at first glance. It helps if one can rearrange the shaded areas.

What I am sharing here may help students who prefer to work with more familiar shapes. It may not be the shortest way.

Interestingly, the rearranged figure looks like a big eye and a small eye.

PSLE students should be familiar with calculating the areas of shaded area within the 3cm square (big eye) and the small eye within the 1cm square.

The area of the shaded area in Q18 is the 2(area of big eye – area of small eye)

Best wishes

http://farm5.static.flickr.com/4085/4988720284_36afd045ba_b.jpg\">

[tiger262]

Respected Uncle Tianzhu,


I am amzed at your tireless energy in conceiving and posting the above drawing. You are helping so many students to do far better in PSLE Maths than they would have done otherwise.

In my view, you and uncle Dharma have at least added 7 to 10 marks to their PSLE aggregate by your contributions in this forum. Not a small feat. You both deserve a ‘big thank you’ from all the students and their parents.

Best regards and grateful thanks.