Q&A - PSLE Math

[Zhu99]

Shimmer:

1)In a online quiz,30 points are awarded for every correct answer. 10 points are deduct for every wrong answer. Alex has 2570 points for answering 103 questions.

How many questions did Alex answer ??? again?

30 x 103 = 3090 --- if 103 Qs answered correctly

3090 - 2570 = 520 --- Marks to be reduced

30 + 10 = 40 --- Marks reduced (lost) by converting 1 correct answer to 1 wrong answer

520/40 = 13 --- No. of Qs answered wrongly

103 - 13 = 90 --- No. of Qs answered correctly

90 x 30 - 10 x 13 = 2570 --- Check and confirm correct

Shimmer:

2)A stall sold 3 kinds of juice. Coconut are at $3,Sugar Cane cost$2 and Guava cost $1.The number of juice sold for 3 data??days?? is in a ratio of 3:6:11,find the average cost each bottle sold during 3 days .?

3 x 3 + 2 x 6 + 1 x 11 = 32

3 + 6 + 11 = 20

32/20 = 1.60

The average cost of each bottle was $1.60.

Shimmer:

3)Owen made 100 sandwich for $100.Chicken are sold for $5 each, fish are sold for $2 and plain are sold for $0.10.How many sandwich did she ??? for each flavor ?

Assume she sold 70 plain sandwich --- 70 x 0.10 = $73 [We need to make an intelligent guess. We may start with 80 ---- but will not get whole number for chicken and fish sandwiches]

100 - 7 = $93

100 - 70 = 30 --- No. of chicken and fish sandwich

30 x 2 = $60 --- if 30 fish sandwich

93 - 60 = $33 --- Amt short

5 - 2 = $3 --- Amt increase if convert 1 fish sandwich to 1 chicken sandwich

33/3 = 11 --- No. of chicken sandwich

30 - 11 = 19 --- No. of fish sandwich

(70 x 0.10) + (19 x 2)+ (11 x 5) = $100 [Check and confirm correct]

70 + 19 + 11 = 100 sandwich [Check and confirm correct]

She sold 70 plain, 19 fish and 11 chicken sandwiches.

Shimmer:

4) A fruit seller had two box of fruits. Each box had mangoes and pears.
The ratio of mangoes tO pear in bOx ??A?? was 5:4. In box B the number of pear was 2/5 of mangoes. The seller transferred half of the pears in A to B.In the end the fruits in A become 105 and the ratio of mangoes to Pear ??? in B or total magoes to total pear??? is 7:4.
A) How many pears were transferred frome A to B?
B)How many fruits are in B in the end?

Box A --- M : P = 5 : 4 ---- 9 u
Box B --- M : P = 5 : 2 ---- 7 p

9 - 2 = 7 u ---> 105
1 u ---> 105/7 = 15

5 p
2 u ---> 15 x 2 = 30

a) 30 pears were transferred from A to B.

b) Information given incomplete / not clear ....?

[kiasuaunt]

MathIzzzFun:

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.

[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: