Q&A - PSLE Math

[bobsg01]

P6 Pie Charts question. :faint:


Appreciate the kind help.

http://i51.tinypic.com/2isxyzd.jpg\">

[Kloggy]

stary:

Kloggy:

Hi,


Need help on following 2 qns from Maha Bodhi, 2010, Prelim.

2) Paper 2, qn 13.
Diagram shows two containers X and Y.
Container X is being filled by tap B
Container Y is being filled by tap A.
Container X has base of 25 cm by length (which is unknown)
Container Y has base of 50 cm by 45 cm

Here is the qn :
In every minute, three times as much water flows out of Tap A as Tap B into two empty containers, X and Y.
After 20 minutes, container X is 2/5 filled with water and the height of the water level in container X is the same as that of container Y.
(a) what is the length of the base of container X?
(b) How many litres of water can container X hold ?

I managed to find the answer to (a), which is 30 cm.
But how to do part (b) ? (Ans : 56.25)

Pls help !!!!!
Thanks.

Base area of Container Y -> 50 x 45 = 2250 cm2
Base area of Container X -> 2250/3 = 750 cm2
Length of Container X -> 750/25 = 30 cm(a)

Time to fill Container X -> 5/2 x 20 = 50 min
Height -> 3/2 x 50 = 75cm
Water to fill Container X -> 25x30x75 = 56250 cm3 = 56.25 litres(b)

Thanks a lot, but I don't understand why the height is 3/2 x 50. Can help to explain ?

[Kloggy]

bobsg01:

P6 Pie Charts question. :faint:


Appreciate the kind help.

http://i51.tinypic.com/2isxyzd.jpg\">

(a) No. of families with 1 or 2 children = 10 + 20 = 30
No. of families with 1,2, 4 or 5 children = 18 x 3 = 54

Therefore,
No. of families with 4 or 5 children = 54 - 30 = 24
No. of families with 3 or more children = 24 + 18 = 42

(b) Total no. of children = 10 + (20x2) + (18x3) + (12x4) + (12x5) = 212

[MathIzzzFun]

Belle2011:

Dear tianzhu and MathIzzzFun,

Thank-you for sharing your solutions.

Cheers,
Belle.

hi Belle2011, u r welcome

cheers.

[bobsg01]

Need some help to explain this as I am a parent who is weak in Math.


I can't explain to my son, when using modeling, when do you know how many unit to used.

In this solution, 3/5 for 10 cents, so you draw 3 units for 5 groups.

But when come to 20 cents, why it's 3 units for 4 groups only? --> how does one determine how many units to used for each group of fraction?

Appreciation any help and thank you. :slapshead:

http://i55.tinypic.com/iokxs1.jpg\">

[corneyAmber]

bobsg01:

Need some help to explain this as I am a parent who is weak in Math.


I can't explain to my son, when using modeling, when do you know how many unit to used.

In this solution, 3/5 for 10 cents, so you draw 3 units for 5 groups.

But when come to 20 cents, why it's 3 units for 4 groups only? --> how does one determine how many units to used for each group of fraction?

Appreciation any help and thank you. :slapshead:

http://i55.tinypic.com/iokxs1.jpg\">

Hi bobsg01,

Based on the diagram, the solution is trying to show that:
3/5 = 9/15 where 9-3 = 6 units remainder
(you see 9 units are shaded)

1/4 = 2/8 where 8-2 = 6 units remainder
(you see 2 units are shaded)

both 6 units remainder are equal because the question says they have the same number of coins after spending 3/5 of 10ct coins and 1/4 of 20ct coins.

This question is tricky in that it requires the child to be able to visualise the same remainder in order to know which multiplier is suitable to create the model units of the same value unlike in common cases you find the common factor(denominator). The key words here are the remaining same number of coins.....

[bobsg01]

Thanks ksi for the enlighenment.


One more part I was unable to explain is the 15 units - 24 (where this no. was calculated from?)

http://i53.tinypic.com/20hlcfs.jpg\">

[corneyAmber]

bobsg01:

Thanks ksi for the enlighenment.


One more part I was unable to explain is the 15 units - 24 (where this no. was calculated from?)

http://i53.tinypic.com/20hlcfs.jpg\">

24 is not calculated.... the question says 10ct coins was 24 more than 50 cts coins so to make it equal to number of 50 cts coins, have to minus 24 away to get an equation.

[bobsg01]

:yikes: So sorry ksi, didn't read carefully enough.


Thanks for the patience and kind explanation ksi.

:imcool: Your Math knowledge are simply cool. :salute:

[corneyAmber]

bobsg01:

:yikes: So sorry ksi, didn't read carefully enough.


Thanks for the patience and kind explanation ksi.

:imcool: Your Math knowledge are simply cool. :salute:

Not a problem, you are most :welcome: