Q&A - PSLE Math

[Drdj]

Hi there,


Please help me with the following :

NanHua Prelim 2008

Qn 24
15 cats can catch 15 rats in 15 minutes. How long does it take 60 cats to cath 60 rats? [Ans = 15 mins - how do you know which qty to stay constant/change]

Qn 44
Amy, Beth and Carrie have some money. If Amy gives $3.50 to Beth, the two girls will have an equal amt of money. If Beth gives $3.50 to Amy, Amy will have thrice as much money as Beth. Carrie's share is the sum of the other two girls. How much money do they have altogether? [Answer = $56]

Misc
David paints once every 2 days. Larry paints once every 3 days.
If the 2 men met on 28th May, what is the earliest date David has to start work? [Answer = 24th May]

Thanks in advance

[tianzhu]

Hi Drdj


You don't have to click on quote each time you want to post new questions.Use it when you want to refer to it.

For new post without referencing, just click on post reply.

[Dharma]

Drdj:

Hi there,


Please help me with the following :

NanHua Prelim 2008

Qn 24
15 cats can catch 15 rats in 15 minutes. How long does it take 60 cats to cath 60 rats? [Ans = 15 mins - how do you know which qty to stay constant/change]

Thanks in advance

15 cats - 15 rats - 15 mins
1 cat - 15 rats - 225 mins
1 cat - 60 rats - 900 mins
60 cats - 60 rats - 900/60 = 15 mins
(Only change 1 independent variable at a time)

[Dharma]

Hi Drdj,


If Amy gives $3.50 to Beth

At last
Amy : 1 unit
Beth : 1 unit
Carrie : 1 part

At first
Amy : 1 unit +$3.50
Beth : 1 unit - $3.50
Carrie : 1 part

If Beth gives $3.50 to Amy

At last[/u]
Amy : 1 unit +$7
Beth : 1 unit - $7
Carrie : 1 part

1 unit + $7 = 3 units - $21
2 units = $28
1 unit = $14

1 part = 2 units = $28

Amt of money 3 of them have = 2 units + 1 part = $28 x 2 = $56

[tianzhu]

Thank you for your help.


RGPS SA2 2008 Q43.


http://www.postimage.org/

[joyceling]

tianzhu:

Thank you for your help.


RGPS SA2 2008 Q43.


http://www.postimage.org/

the answer is 2cm.

[Happygolucky]

HI Tianzhu,


If I’m not wrong , one of the cubes at the uppermost layer was not in the question.

Is the answer 2 cm?

[joyceling]

cubes for each level is (top to bottom ) 1,3,6

water difference between top 2 levels and bottom level is the cubes difference: 8 cubes=1120-352x3=64, so each cube is 8 cm3
so the height is 2cm

[tianzhu]

Happygolucky:

HI Tianzhu,


If I'm not wrong , one of the cubes at the uppermost layer was not in the question.

Is the answer 2 cm?

Hi

This question is from http://www.misskoh.com
Join the free membership to view the question from RGPS.
I guess one of the cube is not in the question as it looks different from the others.

[tianzhu]

Perhaps girls of 2008/9 RGPS would like to comment on the extra cube shown in the picture.


My gut feeling is it’s not there.