Q&A - PSLE Math

[corneyAmber]

http://i724.photobucket.com/albums/ww246/ks2me/P6Aitong.jpg\">

[Dharma]

ksi:

http://i724.photobucket.com/albums/ww246/ks2me/P6Aitong.jpg\">

Thanks ksi for your clear illustration.

[corneyAmber]

Dharma:

Thanks ksi for your clear illustration.

No problem Dharma, just following your instructions. Good way to view it that way.

[visionsg]

My girl is preparing for PSLE and I am confused by the use of "If" in questions. Her teacher tells her one thing, her tuition centre another. And after speaking to a few teachers I know, there is clearly a lack of consistency.


For example:
I make up this question
There are Red and Blue marbles in the ratio 3 : 2. If 10 red marbles are lost, the ratio becomes 1:1. How many Red marbles are there at the end?

In this question, it seems logical that there is no real change to this question and we only use the 10 red marbles to find the answer. The answer would be found like this:
B4
R : B
3 : 2

After
R : B
2 : 2

1units –> 10

There are 30 Red marbles at the end (and beginning) because no change has taken place.

Now what if the question is worded like this.
There are Red and Blue marbles in the ratio 3 : 2 at first. In the end, there is an equal number of Red and Blue marbles. If 10 Red marbles are removed, how many red marbles are there?

For this question, we should have 20 using the final ratio. Correct?

And finally
There are Red and Blue marbles in the ratio 3 : 5. The ratio of the number of Yellow marbles to Blue is 9:4.
a) bla bla bla
b) If 36 Yellow marbles are exchanged for Red and Blue, there would be the same amount of Red and Blue and there would be 50% more Yellow than Red. How many Blue marbles are there?
Before
R : B
3 : 5
12 : 20

Y : B
9 : 4
45 : 20

R : B : Y
12 : 20 : 45 (77 units)

After
R : B : Y
2 : 2 : 3 (7units)
22: 22 : 33 (77units)

How many blue marbles?
20 units –> 20x36 = 720
Correct ?

What if the question is changed to this
a) bla bla
b) If 36 Yellow marbles are exchanged for Red and Blue, there would be the same amount of Red and Blue and there would be 50% more Yellow than Red, how many Blue marbles are there?

Given that the question "how many" is included in the sentence with the comma and not after a full stop, does this change the answer? This is where I get different answers. Some say because of the comma, the question wants an answer assuming it happened.

How to interpret this ??

[firebird]

Dear maths guru


Good morning.

Please help me on the following P6 maths:

1) Melvin, Thomas and Jack put some coins in a piggy bank. They wanted to donate some money to the charity, so Thomas and Jack took out 795 coins. Melvin and Thomas took out 5/13 of the coins from their piggy bank. Jack and Melvin took out 4/5 of the coins from their piggy bank. How many more coins did Thomas take than Melvin?

2) Ali had 5 meter of string. He used 1/4 meter of the string to tie 6 identical parcel. Find the length of the string left after tying 10 such parcels.

3) Find the sum of: 80+82+84+…+158+160
Any short cut instead of writing all and adding them?

4) Mark collected some stamps and put them in two albums. The stamps in album A have a value of 50cents each while the stamps in album B have a value of 10cents each. The total value of stamps in album A was $77.60 more than stamps in Album B. He put 76 more stamps in Album B than in Album A. How much did Mark spend on the stamps in Album B?

Thank you
Firebird

[corneyAmber]

firebird:

3) Find the sum of: 80+82+84+....+158+160
Any short cut instead of writing all and adding them?

I do the easiest one first as I need to scoot off...

80+160 = 240
82+158 = 240
84+156 = 240
:
118+122=240
120

Number of pairs = (118-80)/2 + 1 = (160-122)/2 + 1 = 20
So total = 20*240 + 120 = 4920

[liketoeat]

To all the gurus,


I need clarification for the following question:

5/13 of a rectangular tank, 64 cm long, 30 cm wide and 65 cm high, was filled with water.
a) If 14.4 litre of water is poured into the tank, what would be the height of the water in the tank now?
b) Water is then poured into the tank at the rate of 480 cubic cm per minute. How long would it take for the tank to be completely filled? express your answer in h.

Do we take the height found in (a) to get the answer for (b) or do we treat (a) and (b) separately?

Thank you.

[Dharma]

liketoeat:

To all the gurus,


I need clarification for the following question:

5/13 of a rectangular tank, 64 cm long, 30 cm wide and 65 cm high, was filled with water.
a) If 14.4 litre of water is poured into the tank, what would be the height of the water in the tank now?
b) Water is then poured into the tank at the rate of 480 cubic cm per minute. How long would it take for the tank to be completely filled? express your answer in h.

Do we take the height found in (a) to get the answer for (b) or do we treat (a) and (b) separately?

Thank you.

a)\tHeight of water in tank at first = 5/13 x 65cm = 25cm
New height of water = > 14400cm3/(64cm x 30cm) + 25cm = 32.5cm

b)\tWater is then poured into the tank at the rate of 480 cubic cm per minute.
Need to find volume reqd to fill up tank =.( 64 x30 x 32.5)cm3 = 62,400cm3
Time => 62,400cm3/480cm3/min = 130 min = 2 1/6 hrs

[CoffeeCat]

visionsg:

My girl is preparing for PSLE and I am confused by the use of \"If\" in questions. Her teacher tells her one thing, her tuition centre another. And after speaking to a few teachers I know, there is clearly a lack of consistency.


For example:
I make up this question
There are Red and Blue marbles in the ratio 3 : 2. If 10 red marbles are lost, the ratio becomes 1:1. How many Red marbles are there at the end?

In this question, it seems logical that there is no real change to this question and we only use the 10 red marbles to find the answer. The answer would be found like this:
B4
R : B
3 : 2

After
R : B
2 : 2

1units --> 10

There are 30 Red marbles at the end (and beginning) because no change has taken place.

Now what if the question is worded like this.
There are Red and Blue marbles in the ratio 3 : 2 at first. In the end, there is an equal number of Red and Blue marbles. If 10 Red marbles are removed, how many red marbles are there?

For this question, we should have 20 using the final ratio. Correct?

And finally
There are Red and Blue marbles in the ratio 3 : 5. The ratio of the number of Yellow marbles to Blue is 9:4.
a) bla bla bla
b) If 36 Yellow marbles are exchanged for Red and Blue, there would be the same amount of Red and Blue and there would be 50% more Yellow than Red. How many Blue marbles are there?
Before
R : B
3 : 5
12 : 20

Y : B
9 : 4
45 : 20

R : B : Y
12 : 20 : 45 (77 units)

After
R : B : Y
2 : 2 : 3 (7units)
22: 22 : 33 (77units)

How many blue marbles?
20 units --> 20x36 = 720
Correct ?

What if the question is changed to this
a) bla bla
b) If 36 Yellow marbles are exchanged for Red and Blue, there would be the same amount of Red and Blue and there would be 50% more Yellow than Red, how many Blue marbles are there?

Given that the question \"how many\" is included in the sentence with the comma and not after a full stop, does this change the answer? This is where I get different answers. Some say because of the comma, the question wants an answer assuming it happened.

How to interpret this ??

Unless a question is worded deliberately, otherwise i will take all \"if\" scenarios to mean that the exchange has taken place. Otherwise cue words like \"at first\" or \"in the end\" will be there in the question. If there is any unambiguity ask the teacher during the examination. If it is valid they will notify the school student cohort (assuming school examination not sure about psle).

[Dharma]

firebird:

Dear maths guru


Good morning.

Please help me on the following P6 maths:

1) Melvin, Thomas and Jack put some coins in a piggy bank. They wanted to donate some money to the charity, so Thomas and Jack took out 795 coins. Melvin and Thomas took out 5/13 of the coins from their piggy bank. Jack and Melvin took out 4/5 of the coins from their piggy bank. How many more coins did Thomas take than Melvin?

2) Ali had 5 meter of string. He used 1/4 meter of the string to tie 6 identical parcel. Find the length of the string left after tying 10 such parcels.

3) Find the sum of: 80+82+84+....+158+160
Any short cut instead of writing all and adding them?

4) Mark collected some stamps and put them in two albums. The stamps in album A have a value of 50cents each while the stamps in album B have a value of 10cents each. The total value of stamps in album A was $77.60 more than stamps in Album B. He put 76 more stamps in Album B than in Album A. How much did Mark spend on the stamps in Album B?

Thank you
Firebird

Q1)
Melvin & Thomas => 5/13
Jack & Melvin => 4/5
Jack & Thomas = > 2 – 5/13 – 4/5 = 53/65
53u = 795
1u = 15
4/5 x 795 = 636
Diff = 795 – 636 = 159

Q2)
Length of string to tie 10 parcels = 10 x (1/4)/6 = 5/12m
Balance of string left = (5 – 5/12)m = 4 7/12 m

Q3)

2[1 + 2 + … + 80] – 2[ 1+ 2 + …+ 39]
= 2[ (80 X 81)/2] – 2[ (39 X 40)/2]
= 2 X 40/2 [162 – 39]
= 4920

Q4)
A : (1u)(50¢)
B : (1p)(10¢)

1p – 1u = 76 ……………………..(1)
(1u)(50¢) – (1p)(10¢) = 7760¢ ………..(2)

1p(50¢) – (1u)(50¢) = 3800¢ …………(1) x 50¢ = (3)

(2) + (3)
1p(40) = 11560
1p = 289

Amt spend on B => 289 X 10¢ = 2890¢ = $28.90