Q&A - PSLE Math

[kuts]

tianzhu:

kuts:

Help please.... from Tao Nan Prelims 2012

Thanks Tianzhu for the simplified explanation



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

[kuts]

ksme:

kuts:

Can anyone help me to solve the qn no. 29 of Tao Nan 2012 Prelims.

Thanks ksme. I could understand now from ur explanation

Thanks in advance

Hi,
Is this the ribbon question? If yes, here's the solution:

Vertical sides = 4*22cm = 88cm
top and bottom sides =2*(15+20)=70cm
Ribbon used to tie the bow = 200-88-70=42cm
Answer = 0.42m

[tianzhu]

peggy:

Please assist with this.


Ken and Peter went shopping with a total of $90. Ken spent twice as much as Peter. Ken had spent $5 more than the amount that he had left. In the end, Peter had thrice as much money left as Ken.

A) how much money did Peter spend?
B) how much money did Ken have at first ?

Thanks!

Hi

Good Morning.

You may use MD or units.

I’ll give some pointers due to time constraints.

1) Draw 2 boxes to show ken’s spending and 1 box for Peter’s spending.

2) Draw a box (bigger than (1)) to show Ken’s remaining money, this box is 5 less than the 2 boxes in (1).Similarly draw 3 boxes to show Peter’s remaining money.

From the MD, 11 boxes (1) ----- 90 + 20 ------ 110

1 box ------ 10

Peter@spending ------- $10

Ken@first ------ $35

If you need the MD, please let me know.

Best wishes

[dicoyote]

Hi,


Seeking help for these questions, thanks in advance

1) Mrs Leong had white and orange ping pong balls in the ratio 7:5. She then replaced several white ping pong balls with orange ones keeping the total number of ping pong balls the same. The ratio of the number of white ping pong balls to orange ping pong balls became 3:5.
(a) If the total number of ping pong balls is not more than 30, how many white ping pong balls did Mrs Leong have at first? (My answer is 14, not sure if its correct)
(b) How many new orange ping pong balls were used to replace the white ones? (My answer is 5)

2) Peter used two taps to fill an empty rectangular tank with water. The first tap could fill the tank completely in 2 hours, the second tap in 6 hours. At first he turned on only the first tap. 20 minutes later, he turned on the second tap as well. How long did Peter take to fill the tank to the brim with water?

3) Terence was driving from King’s Gardens to Queen’s Park. Halfway to his destination, his car passed Sally’s car which is travelling at 84km/h in the opposite direction. 1 1/3h later, Terence reached Queen’s Park while Sally was still 10km away from King’s Gardens.
(a) What was the distance between King’s Gardens and Queen’s Park?
(b) What was the average speed that Terence was travelling?

[tianzhu]

dicoyote:

Seeking help for these questions, thanks in advance

1) Mrs Leong had white and orange ping pong balls in the ratio 7:5. She then replaced several white ping pong balls with orange ones keeping the total number of ping pong balls the same. The ratio of the number of white ping pong balls to orange ping pong balls became 3:5.
(a) If the total number of ping pong balls is not more than 30, how many white ping pong balls did Mrs Leong have at first? (My answer is 14, not sure if its correct)
(b) How many new orange ping pong balls were used to replace the white ones? (My answer is 5)

Hi

We have the same answers of 14 and 5.

Best wishes

[tianzhu]

xiaotiao:

Can anyone help me to solve this problem, thanks!!!


The average weight of a group of boys is 50kg. If one more boy who weighs 76 kg joins the group, the average of weight will become 52kg. Find the number of boys in the group.

Hopefully a kind soul can do me a favour.

Hi

52 – 50 ----- 2

76 – 52 ----- 24

Number of boys in the group ------- 24/2 ------- 12

Best wishes

[tianzhu]

dicoyote:

2) Peter used two taps to fill an empty rectangular tank with water. The first tap could fill the tank completely in 2 hours, the second tap in 6 hours. At first he turned on only the first tap. 20 minutes later, he turned on the second tap as well. How long did Peter take to fill the tank to the brim with water?

Hi

Use a common multiple of 6.

In 1h, first tap ------ 3 units

In 1h, second tap ------ 1 unit

In 20 minutes after he turned on the first tap, the water level in the tank is 2 units.

Hence, remaining amount of water required to fill tank to brim ------ 4 units

In 1h, first tap and second tap ------ 4 units

Therefore time taken ------ 4/4 ------ 1h

Total time taken@Peter ------- 1h 20 minutes

Best wishes

[peggy]

Hi Tianzhu,


Thanks for the solution for Ken n Peter’s problem.

Cheers!

[nounou]

Please help to solve this Q :yikes: :?:

Q10 from Nanyang Prelim 2012. :gloomy:
Answer given = 266 2/3 m
:thankyou: :thankyou: :thankyou: http://i49.tinypic.com/30nfdja.jpg\">

[nounou]

Treelodge:

Please help to solve this Q :yikes: :?:

Q10 from Nanyang Prelim 2012. :gloomy:
Answer given = 266 2/3 m
:thankyou: :thankyou: :thankyou: [IMG]http://i49.tinypic.com/30nfdja.jpg\">

http://i49.tinypic.com/30nfdja.jpg\">