Q&A - PSLE Math

[bluesky63]

small:

Hi fxchow,


HTH but I am not so sure on my answer for part (b).

a)
Given that 30% of the pupils in Sch A is 45 more than 40% of the pupils in Sch B.
0.3A - 45 = 0.4B --> x10

3A = 4B + 450 ----- equation (1)


If 10% of the pupils in Sch A leaves to join Sch B, there will be 200 more pupils in Sch A than Sch B
0.9A – 200 = 0.1A + 1B
0.8A = 1B + 200 --> x10

8A = 10B + 2000 ----- equation (2)


We will need to eliminate A to get B;

equation (1) x 8:
24A = 32B + 3600

equation (2) x 3:
24A = 30B + 6000

32B + 3600 = 30B + 6000
2B – 6000 – 3600
2B = 2400
1B = 1200

There are 1200 pupils in Sch B


b)
from equation (1) :

3A = 4 X 1200 + 450
3A = 4800 + 450
3A = 5250
1A = 1750 (100%)

The different between School A and School B is:
1750 – 1200 = 550

1750 = 100%
550 = 550/1750 x 100%
= 1100 / 35 %
= 31 3/7%


There are 31 3/7% percent less pupils in Sch B than Sch A

Hi, can anybody show us the working using modelling (blocks) Thanks !

[P5G]

htn:

P5G:

[quote=\"htn\"]Hi Vanilla Cake


Can u teach me how to solve nan hua prelim paper 2 Q16 b?
TIA

Hi Uncle/Auntie htn,

For (16b), you just need to add the two areas together then use the volume
of water divide by the total area as follows:

500 + 300 = 800 cm2

6000/800 = 7.5 cm

P5G

Thanks

Auntie htn[/quote]
Hi htn,

I am sorry that P5G has given you the wrong volume. She should not have used 6000 cm3 that she worked out in part (a). The volume should be the amount flowed out from Tap B only and not the net volume from the tank.

The volume should be 800 x 20 = 16 000 cm3.

Combined area = 300 + 500 = 800 cm2

Height of water in 2 containers = 16 000 / 800 = 20 cm


P5G mum.

[kavisuresh]

Thank you Tianzhu !

[tianzhu]

kavisuresh:

Thank you Tianzhu !

Hi

You're welcome.

CHS SA2 Q15 2010

As in any speed question, it’s useful to translate words into picture. Draw a line diagram.

In 1h John travelled 4km or 4000m faster than Mary. This means Mary is 2000m away from the midpoint.

2000m ------- 60min (1h)
100m ------- 3min
300m -------9min

They met at 9.09 am

John took 3 min and Mary took 9 min to travel the same distance.John was 3 times faster than Mary.

If John took 9 min, then Mary would take 27min
Total time taken by Mary ------36min

Mary would reach point B @ 9.36am

Best wishes

[htn]

[quote="P5G

[/quote]


Hi htn,

I am sorry that P5G has given you the wrong volume. She should not have used 6000 cm3 that she worked out in part (a). The volume should be the amount flowed out from Tap B only and not the net volume from the tank.

The volume should be 800 x 20 = 16 000 cm3.

Combined area = 300 + 500 = 800 cm2

Height of water in 2 containers = 16 000 / 800 = 20 cm


P5G mum.[/quote]


Thanks P5G mum

[htn]

Hi, please help.


Amanda has $280 more than John. After Amanda spent 20% of her money and John spent 50% of his money, Amanda has $260 more than John in the end. How much does John have at first?

TIA

[tianzhu]

htn:

Hi, please help.

Amanda has $280 more than John. After Amanda spent 20% of her money and John spent 50% of his money, Amanda has $260 more than John in the end. How much does John have at first?

Hi

You may use MD or UM.

At first
Amanda ------ 10 units + 280
John ------ 10 units

Spent
Amanda ------ 2 units + 56
John ------ 5 units

In the end ---- Left
Amanda ------ 8 units + 224
John ------ 5 units

Amanda has $260 more than John in the end.

8 units + 224 ----- 5 units +260

3 units ------36
1 unit -----12

John ------10 units ------10*12 ------120

Best wishes

[kavisuresh]

Pls explain the basis for selecting numbers for the following qn.


qn: The diagram below shows 2 different views of the same cube. The numbers on the faces of the cube are 1,2,3,4,5 aned 6. Fill in the missing numbers in the net below.
http://i56.tinypic.com/104hxrp.jpg\">

thanks.

[kavisuresh]

Please explain the solution:

1. Study the five layer block as shown below. It is built from 55 similar 1cm cubes and is painted green. Find the total surface area that is painted green.
http://i54.tinypic.com/s6nhtt.jpg\">


2.James had a box of Australia and Japan stamps. After losing 4 Australian stamps, 20% of remaining stamps were Australian stamps. When he lost another 6 Australian stamps and gave away 78 Japan stamps, 1/3 of what he had left were Australia stamps. How many stamps had he at first ?
(pls expl model and ratio method)

Thank you.

[kavisuresh]

Pls help to solve.

1. There are ___ hundredths in 186.42
(42 / 18642 / 2)

2.Mrs. Tan baked 60 more chocolate pies than banana pies. After she gave away 2/5 of the chocolate pies and 3/4 of the banana pies, she was left with 64 more chocolate pies than banana pies. How many chocolate pies did she bake at first ?

3. Gerald had $20 more than Tommy at first. After Gerald gave Tommy $60, Gerald had 1/3 as much money as Tommy. Find amt of money Gerald had at first ?

4. Krishnan spent $84 on some plates and 1/3 of remaining money on some cups. If he had 1/5 of original sum of money left, how much did she have at first ?
Thanks a lot.