Q&A - PSLE Math

[tianzhu]

millan:

Pls help to solve this:


The ratio of no of 20cents coinys to the no of 1 dollar coins in a container was 1:4 . 6 1 dollar coins were taken out of the container and exchanged foe 20 cent coin which were put into the container. The ratio of the no of 20 cents coins to the no of 1 dollar coin became 3:5 . How much money was there in the container.

We got $100.8 (ans not known yet) by algebra, qn is can this be solved by model?

Thks

Hi

Good Morning.

I did a quick check and the answer is $100.80.

You may work out this question from two perspectives, one in term of numbers of coins and dollar notes and the other in term of the value of money.

There are some similar types of questions in earlier posts in this thread.

Yes, you may use MD, Units and Parts or Systematic Listing.

Best wishes

[millan]

tianzhu:

millan:

Pls help to solve this:


The ratio of no of 20cents coinys to the no of 1 dollar coins in a container was 1:4 . 6 1 dollar coins were taken out of the container and exchanged foe 20 cent coin which were put into the container. The ratio of the no of 20 cents coins to the no of 1 dollar coin became 3:5 . How much money was there in the container.

We got $100.8 (ans not known yet) by algebra, qn is can this be solved by model?

Thks

Hi

Good Morning.

I did a quick check and the answer is $100.80.

You may work out this question from two perspectives, one in term of numbers of coins and dollar notes and the other in term of the value of money.

There are some similar types of questions in earlier posts in this thread.

Yes, you may use MD, Units and Parts or Systematic Listing.

Best wishes

Can u show me in any of the above? thks

[tianzhu]

millan:

Can u show me in any of the above? thks

Hi

Please go to page 310 of this thread.

http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&hilit=value+of+money&start=3090

Best wishes

[millan]

tianzhu:

millan:

Can u show me in any of the above? thks

Hi

Please go to page 310 of this thread.

http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&hilit=value+of+money&start=3090

Best wishes

I actually tried using the coin example it comes to a stage where the per unit is in decimal.. abit weird..

[tianzhu]

millan:

[I actually tried using the coin example it comes to a stage where the per unit is in decimal.. abit weird..

Hi

A quick one.

6 $1 notes ------ $6 ------- 30 20cents coins

At first ----- 20cents:$1 ------- 1unit : 4units
Change -----20cents:$1 ------- +30 : -6
In the end --- 20cents:$1 ------- 3 parts : 5parts

Equalising the final parts or cross multiply

5 units + 150 ------ 12 units – 18
7 units ------ 168

1 unit ------ 24

20cents ----- 1 unit ------24*0.2 ------ 4.8

$1 ------- 4 units ------- 96*1 ------96

Hence, total amount is $100.8

You may read up more on Units and Parts by reading Challenging Maths Made Easy by Ammiel Wan.

Best wishes

[pixiedust]

Karen and David had $127 altogether. Karen spent 1/3 of her money on a toy and David spent 3/5 of his money on food. If David spent $9 more than Karen, how much money did Karen have at first ?


I solved using simultaneous equations (from model) and unitary method.
For unitary method, I can get the right answer but I can't explain how to handle the $9.

Appreciate any help with (1) pure model/pictorial solution (2) unitary method with reasoning of how the $9 is handled.
Thanks very much !

[MathIzzzFun]

pixiedust:

Karen and David had $127 altogether. Karen spent 1/3 of her money on a toy and David spent 3/5 of his money on food. If David spent $9 more than Karen, how much money did Karen have at first ?


I solved using simultaneous equations (from model) and unitary method.
For unitary method, I can get the right answer but I can't explain how to handle the $9.

Appreciate any help with (1) pure model/pictorial solution (2) unitary method with reasoning of how the $9 is handled.
Thanks very much !

Hi

this MD should help..

http://i40.tinypic.com/16la521.jpg\">

cheers.

[shin88]

Hi,


Does anyone has the question for Nanyang Ca1 paper 2 Q18 .
The underline part is missing in the exam paper.

The total area of Triangle A and Triangle B is _______ of the area of Triangle C.

Thanks in advance.

[pixiedust]

Thanks MathsIzzzFun ! *banghead* so easy yet I can't see it !


shin88, it is 125%. see here -> http://www.kiasuparents.com/kiasu/forum/viewtopic.php?p=691764#p691764

[tianzhu]

pixiedust:

For unitary method, I can get the right answer but I can't explain how to handle the $9.

Hi pixiedust

Good Morning.

I am wondering what you mean by using unitary method.

The unitary method involves the finding of a value equivalent to one unit. Then use this value to find the value of more units. In a way, the working in MD is quite similar; we are also using the unitary method.

An example of using unitary method.

110% of Science score ------ 88
1% of Science score ----- 88/110
100% of Science score ----- 88/110*100 ----- 80

110 units ------ 88
1 unit ------ 88/110
100 units ----- 88/110*100 ------ 80

Best wishes