Q&A - PSLE Math

[pixiedust]

Shimmer,


You can check this : http://www.kiasuparents.com/kiasu/forum/viewtopic.php?p=132258#p132258

For your question 1 :
An empty rectangular tank is being filled with water from Tap A at 1 liter per min. Tap B drains water out from the tank at 800cm cubic per min. How long will it take for the water level to reach a height of 10cm if both the taps are turned on at the same time ? Length is 40cm and breath is 20cm.

To reach height of 10cm,
Volume required = 40cm*20m*10cm=8000cm3

In 1 minute,
Tap A adds 1000cm3, Tap B drains 800cm3
Hence, net gain is 200cm3

To reach 8000cm3 -> 8000cm3/200cm3=40minutes

[tianzhu]

pixiedust:

Need help with (b) Calculate the difference between shaded area 'A' and 'B'.

Thanks !

http://i1197.photobucket.com/albums/aa424/pixie_dust8/mq4.jpg\">

Hi

Difference in shaded area ------ Area of circle (r6) – area of triangle (base 10cm and height 12cm)

Divide the above answer by 2 to get (A-B)

Best wishes

[tianzhu]

jewelbox:

How do i solve this psle qn without using guess and check? thks.

A fruit stall sold pears at 70cents each and apples at 40 cents.
Sally bought some pears and Tom bought some apples from the fruit stall.
Sally spent $1.10 more than Tom, but had 7 fruits fewer than Tom.
a) How many pears did Sally buy?
b) how much did tom spend on the apples?

Hi

There are a few approaches to do this question.

There are 7 more apples than pears.

Imagine Sally buying 7 more pears

This will add 7*70 ------ 490 cents

110 + 490 ----- 600

Difference between a pear and an apple ------ 30 cents

Number of apples ------ 600/30 ------ 20

Number of pears ------- 20 - 7 ------ 13

20*0.4 ------- 8 (amount spent on apples)

Best wishes

[Spongy]

tianzhu:

Spongy:

Hi I need help in this question. Please help. Thanks.


1. 500 people paricipated in a contest. 105 of them were adults and the rest were children. 3/5 of boys and 5/7 of the girls were Singaporeans while the rest of the children were foreigners. There were 10 more foreign girls than foreign boys. How many Singaporean children were there?

Hi

This question touches on simultaneous concept.

You may use MD, “Units and Parts” or use letters of the alphabet to show the variables.

Number of children ------- 500 – 105 ------ 395

Boys

Singaporean ------- BBB
Foreigner ------ BB

Girls

Singaporean ------- GGGGG
Foreigner ------ GG

GG ------ BB + 10
G ----- B + 5

BBBBB + BBBBBBBBBBBB + 35 -------- 395 (12B + 35 ------ 395)

B ------ 30
G ------ 35

Number of Singaporean children ----- 90 + 175 ------ 265

Best wishes

Hi Tianzhu, thanks a lot, however I do not understand from
BBBBB + BBBBBBBBBBBB + 35 .......... onwards

[tianzhu]

Spongy:

Hi Tianzhu, thanks a lot, however I do not understand from

BBBBB + BBBBBBBBBBBB + 35 .......... onwards

Hi

Good Morning.

I am using letters of the alphabets to represent the boxes in MD.

BBBBB + BBBBBBBBBBBB + 35 -------- 395

This means 12B + 35 ------ 395 (normally expressed as in simultaneous equations)

If you use MD, we’ll 12 boxes + 35 ------ 395

This means 12B or 12 boxes ------ 395 – 35 ------ 360

Hence, 1B or 1 box ------ 360/12 ------ 30

Best wishes

[kiasuaunt]

Winx5015:

Thanks kiasuaunt and tianzhu. Have a nice weekends

You are most welcome.

[MathIzzzFun]

Spongy:

Hi I need help in this question. Please help. Thanks.


1. 500 people paricipated in a contest. 105 of them were adults and the rest were children. 3/5 of boys and 5/7 of the girls were Singaporeans while the rest of the children were foreigners. There were 10 more foreign girls than foreign boys. How many Singaporean children were there?

Hi

using MD (can be directly translated to \"units\" approach)..

http://i47.tinypic.com/331m648.png\">

cheers.

[jewelbox]

Thanks Tianzhu.

[shurley197323]

Hi, can someone help on these 2 RGS 2011 prelim questions No 17 & 18.

No 18: Beaker A & Beaker B contain some water. If 46.5ml of water is drained out from beaker A, the volume of the water in beaker A will be 60% that of the water in beaker B.
If 35.2ml of water is drained out from beaker B, the volume of the water in beaker B will be 85% that of the water in beaker A.
What is the total volume of water in beaker A & beaker B ?

[MathIzzzFun]

shurley197323:

Hi, can someone help on these 2 RGS 2011 prelim questions No 17 & 18.

No 18: Beaker A & Beaker B contain some water. If 46.5ml of water is drained out from beaker A, the volume of the water in beaker A will be 60% that of the water in beaker B.
If 35.2ml of water is drained out from beaker B, the volume of the water in beaker B will be 85% that of the water in beaker A.
What is the total volume of water in beaker A & beaker B ?

Q17- http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=6840

Q18- http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&p=787503&hilit=Beaker+A#p787503

cheers.