Q&A - PSLE Math

[underthesea]

s :shock:

tianzhu:

kuts:

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?

[zanen]

sorry can help with this? hw tmr.

find the value of 23+24+25...+99

[MathIzzzFun]

underthesea:

s :shock:

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.

[MathIzzzFun]

zanen:

sorry can help with this? hw tmr.

find the value of 23+24+25...+99

(23+99) x (99-22)/2 = 4697

or
sum of (1+2+3+4...+98+99) - sum of (1+2+3+...21+22)
= 4950-253=4697

cheers.

[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%.