Q&A - PSLE Math

[underthesea]

MathIzzzFun:

underthesea:

s :shock: [quote=\"tianzhu\"]]Help please.... from Tao Nan Prelims 2012


1. There was some water in a container. Felicia first poured out 1/2 of the water. The she poured out 1/3 of the remaining water. In the third pouring, she poured ouot 1/4 of the remaining water and so on. How many times pouring will there be for the remaining water to be exactly, 1/10 of the original amount of water in the container?


Thanks in advance!
Hi

Try to see the pattern of 1/(n+1) for the remaining amount of water, where n refers to the number of pourings

In this case, it’s the 9th pouring. Best wishes

TianZhu,

I still don't understand this, can help to elaborate?

My DD has a similar question:

Mrs Wong had 2000 sweets. She gave all the sweets to her children. On the 1st day, the children ate 1/2 of the sweets. Her children continues to eat 1/3, 1/4, 1/5, ....1/2000 of the remaining sweets from the previous day. How many sweets were left at last?

after 1 pour, remainder --> 1-1/2=1/2 of original
after 2 pours, remainder --> 1/2 - 1/3 x 1/2 = 1/3 of original
after 3 pours, remainder --> 1/3 - 1/4x1/3 = 1/4 of original

after N pours, remainder --> 1/(N+1) of original
or
after (N-1) pours, remainder --> 1/N of original

to get 1/10 of original amount of water --> after (10-1)= 9 pours

cheers.[/quote]Thank you so much. I can see the pattern now. :salute:

[mummy so kiasu]

I did not get the 2012 Prelim papers for my boy. He has too many homework from his school. Can anyone kind enough to share the 4/5 marks questions from NYPS or RGPS?

[kiasuaunt]

mummy so kiasu:

I did not get the 2012 Prelim papers for my boy. He has too many homework from his school. Can anyone kind enough to share the 4/5 questions from NYPS or RGPS?

Hi - god-dd's school exchange prelim papers with RGS - will share when she gets them. Treelodge had posted a few killer questions from NYPS and one from RGS already.

[mummy so kiasu]

kiasuaunt:

mummy so kiasu:

I did not get the 2012 Prelim papers for my boy. He has too many homework from his school. Can anyone kind enough to share the 4/5 questions from NYPS or RGPS?

Hi - god-dd's school exchange prelim papers with RGS - will share when she gets them. Treelodge had posted a few killer questions from NYPS and one from RGS already.

Thanks kiasuaunt, I have managed to find a few on page 797, 798 & 801. :thankyou:

[Zhu99]

kiasuaunt:

MathIzzzFun:

[quote=\"AJH\"]Hi. I nd help with this ques.


Brendan and Raidah saved $6475.60 altogether. 2/5 of Brendan's savings was $341.50 more than 1/5 of Raidah's savings. How much more money than Brendan did Raidah save?

Can't seem to get the ans - $1020.20. Thank you.

1/5 of Raidah's savings --> 2 units,
Raidah's savings --> 10 units
2/5 of Brendan's savings --> 2 units + $341.50 = 2 x (1 unit + $170.75)
Brendah's savings --> 5 units + $853.75

Total --> 15 units + $853.75 = $6475.60
5 units --> $1873.95

Raidah's savings MINUS Brendan's savings
= 5 units - $853.75
= $1873.95 - $853.75 = $1020.20

cheers.

Hi - sorry for being so slow :scratchhead: is it possible to explain by MD? Thank you.[/quote]B --- 5 u
R --- 5 p

5 u + 5 p ---> 6475.60
2 u ---> 1 p + 341.50

1 u + 1 p ---> 6475.60/5 = 1295.12
1 p ---> 1295.12 - 1 u

2 u ---> 1295.12 - 1 u + 341.50
3 u ---> 1636.62
5 u ---> 1636.62/3 x 5 = 2727.70

5 p ---> 6475.60 - 2727.70 = 3747.90

3747.90 - 2727.70 = 1020.20

Raidah saved $1020.20 more than Brendan.

[Zhu99]

MathIzzzFun:

Clairifina:

Hi, can somebody please help with this question? It will be much appreciated. Thank you in advance!


Store X sells an ipad at $660 which is 20% more than the price at store Y. During The Great Singapore Sale, both stores offered the same percentage discount for the iPad. Mr Lee bought the iPad from store Y and paid $104.50 less than the discounted price at store X. What is the percentage discount?

20/120 x $660 = $110 --> Price of the ipad at Store X is $110 more than that at Store Y.

$104.50/$110 x100% =95%
Discount -->110%-95% = 5%

cheers.

120/20 x 104.50 = 627 --- Discount price at Store X

660 - 627 = 33 --- Dollar discount

33/660 x 100% = 5%

The percentage discount is 5%.

[kwcllf]

Sorry, don’t have the diagram to show.


For a Triangular pyramid:
The first level needs 3 sticks to form (1 single triangle)
The second level needs 9 sticks to form (2 triangles as base)
The Third level needs 18 sticks to form (3 triangles as base)
The fourth level needs 30 sticks to form (4 triangles as base) …etc

How many sticks are needed to form a 10-level pyramid?

Thanks

[Zhu99]

kwcllf:

Sorry, don't have the diagram to show.


For a Triangular pyramid:
The first level needs 3 sticks to form (1 single triangle)
The second level needs 9 sticks to form (2 triangles as base)
The Third level needs 18 sticks to form (3 triangles as base)
The fourth level needs 30 sticks to form (4 triangles as base) .........etc

How many sticks are needed to form a 10-level pyramid?

Thanks

1 --- 3 x 1
2 --- 3 x 1 + 3 x 2 = 3 x (1+ 2) =9
3 --- 3 x 1 + 3 x 2 + 3 x 3 = 3 x (1 + 2 + 3) = 18

10 --- 3 x (1 + 2 + 3+ 4 + 5 + 6 + 7 + 8 + 9 + 10) = 3 x 55 = 165

165 stickers are needed to form a 10-level pyramid.

[24hr_mum]

can someone explain to me nanyang paper 2 q17.

[kwcllf]

Hi Zhu99,


Thanks very much!