Q&A - PSLE Math

[its888me]

speedmaths.com:

its888me:

[quote=\"its888me\"]So sorry, another question from Nanyang prelim 2010 again, Q11:


Diagram A shows a closed rectangular tank of dimensions 20cm by 20cm by 40cm with a cube of edge 10cm glued to its bottom left corner. The tank contains 12 litres of water.

Diagram B shows the same rectangular tank lying on its side. Find the height of the water level, in cm, corrected to 2 decimal places.

http://i48.tinypic.com/302o09z.jpg\">

Again, TIA!

Can someone help with this question? My child assumed that in the Diagram B, the water level reached at the 1/2 point at the cube, thus, getting the answer 14.36cm. Given answer is 15.71.

Again, thanks a lot!

Hi,

Let's try this method:

First,
find the \"Volume of Air\" at top part of Diagram A.
(Vol of air) = (Vol of tank) - (Vol of water) - (Vol of cube).

Next,
find height (or depth) of air at top of Diagram B.
(Height of air) = (Vol of air) / (nett Base Area)
nett Base Area = (40 x 20) - (10 x 10)

Finally,
Height of water = 20 cm - (height of air)

Can you work from here?

Hope this helps.

Cheers

speedmaths.com


.[/quote]Thanks speedmaths.com! Will try to work it out. Many thanks!

[Recia Lim]

Please help to solve this speed question. Thanks!

Question: Mrs Tan took 40 min to walk from her home to the market. On her return journey, she took an additional 8 min. her speed on the way back was 1km/h slower. What was the distance between her home and the market?

[Michaelia0816]

tianzhu:

Michaelia0816:

My answer for this is 960, but I do checking, I found out it is wrong so I really really dun know do this question.

Hi

If you work based on the question, you would get an answer of 960.

However when you plugged back to check, it defied logic.

Please check your question.

Best wishes

Hi! Thx you for helping my pervious question, I decided to use SL for it as I not really used to Units and Parts question, but I will try to use more of it often later on since it is common on hard question. But I still cannot get the balloons question right, can you teach me?
:thankyou:

[tianzhu]

Recia Lim:

Please help to solve this speed question. Thanks!

Question: Mrs Tan took 40 min to walk from her home to the market. On her return journey, she took an additional 8 min. her speed on the way back was 1km/h slower. What was the distance between her home and the market?

Hi

There are a few ways to do this question.

For this question, students may get their answers quickly using GC.

Another possibility is to use inverse proportion if students are familiar with it.

Given the same distance, speed is inversely proportional to time.

Higher speed needs less time.

Lower speed leads to more time.

Time ratio

40:48 ------- 5:6

Speed ratio ------- 6:5

1 unit ------ 1 km/h

5 units ------ 5 km/h

Distance between her home and the market ------- 5*48/60 ------- 4 km

Alternatively you may use the faster speed of 6 km/h

In this case, 6*40/60 ------ 4 km.

Best wishes

[tianzhu]

Michaelia0816:

Hi! Thx you for helping my pervious question, I decided to use SL for it as I not really used to Units and Parts question, but I will try to use more of it often later on since it is common on hard question. But I still cannot get the balloons question right, can you teach me?
:thankyou:

Hi girl

Try to learn UP as it offers you another approach.

As for the ballon question, as I mentioned earlier, please check your source to ensure that the question is in order.

Best wishes

[Michaelia0816]

ok.

[2632parent]

Need help on this question


1) The cost of 3 apples is the same as the cost of 2 oranges. The total cost of 4 apples and 3 oranges is $3.40. Mrs tan bought 7 apples and 5 oranges. How much did she pay for the apples and oranges altogether?

Thank you

[tianzhu]

2632parent:

Need help on this question


1) The cost of 3 apples is the same as the cost of 2 oranges. The total cost of 4 apples and 3 oranges is $3.40. Mrs tan bought 7 apples and 5 oranges. How much did she pay for the apples and oranges altogether?

Thank you

Hi

You may use MD or work with units.

1 apple ----- 2 units

1 orange ----- 3 units

4*2 + 3*3 ------- 17 units

17 units ------- 340

1 unit ------ 20

Mrs Tan bought 7 apples and 5 oranges.

7*2 + 5*3 ------ 29 units

29*20 ------ 580

She paid $5.80

Best wishes

[2632parent]

Thank you councillor for your speedy reply, sorry I have another question for you.


1) Packet A, Packet B and Packet C each contained some salt. At first, there were 200g more salt in Packet A than Packet b. Packet C had 3/4 of the amount of salt in Packet A. After 1/8 of the amount of salt in Packet A was transferred to Packet B, there was 82.15g of salt in Packet B. How many percent less salt were there in Packet C than in Packet A at first?

Many many thanks

[tianzhu]

2632parent:

Thank you councillor for your speedy reply, sorry I have another question for you.


1) Packet A, Packet B and Packet C each contained some salt. At first, there were 200g more salt in Packet A than Packet b. Packet C had 3/4 of the amount of salt in Packet A. After 1/8 of the amount of salt in Packet A was transferred to Packet B, there was 82.15g of salt in Packet B. How many percent less salt were there in Packet C than in Packet A at first?

Many many thanks

Hi

Packet C had 3/4 of the amount of salt in Packet A.

A ------ 4 units

C ------- 3 units

C ------- 1 unit less than A

% ------- ¼*100% ------- 25%

Best wishes