Q&A - PSLE Math

[Pen88n]

pixiedust:

Hi Tianzhu, thanks. It is from worksheet given by ds's school.

May I know the thinking process to derive the answer ?

I am not Tianzhu, but maybe I can help to clarify how to derive the answer.

The 1st clue comes from A x 4 = D. D is a single digit number, so A can only be 1 or 2. Again D x 4 = a number with a last digit A. By substituting 1 and 2 into the 2 equations, you can derived that A = 2 and D = 8

Now that we know A = 2 and D = 8, we also know that B x 4 = C, C will be a single digit, so B is 1 and C is > 4. C x 4 + 3 = a number that ends with a digit 1. By substituting, you will find that C = 7

[MathIzzzFun]

pixiedust:

Hi Tianzhu, thanks. It is from worksheet given by ds's school.

May I know the thinking process to derive the answer ?

Hi

Just to add some points. Two concepts will be useful in solving this puzzle :
1. Any number x even number = even number
2. Even number + ODD number = odd number


http://postimage.org/image/2ia1jqch0/


cheers.

[pixiedust]

Thank you Pen88n & MathIzzzFun ! I need a bit of time to think through your explanations but they surely helped. Thanks very much !

[ozora]

tianzhu:

ozora:

Is my model correct? and I got stuck.

D [ 40 ][ 70]
A [20][ ]

D [20][ 130 ]
A [20][20][ ]

Hi ozora.

Good Morning.

This is a question involving “case1 case 2 scenarios”.

In doing this question, it’s important to note that the number of words to be learnt by Doris and Annie remains the same in both cases.

The first slide shows the thought process. You may use MD or UM to solve this question. In this case, I am using the MD way. As usual, I am drawing more models than necessary to show the flow of events.

Hope this helps.

Best wishes

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thanks for the guide

[ozora]

MathIzzzFun:

ozora:

Need guidance.

Doris and Annie have each planned a list of words to learn,
If Doris learnt 40 words per day while Annie learnt 20 words per day, Doris would have 70 words left to learn while Annie had completed learning all the words.
If Doris learnt 20 words per day while Annie learnt 40 words per day, Doris would have 130 words left to learn while Annie had completed learning all the words.
How many words do Doris and Annie have to learn respectively?

Is my model correct? and I got stuck.

D [ 40 ][ 70]
A [20][ ]

D [20][ 130 ]
A [20][20][ ]

Hi

MD is as follows:

[] =words learnt

Scenario 1
D [][][][][70]
A [][]

Scenario 2
D [][130]
A [][]

Comparing the models for \"D\"
[][][] = 60
[] = 20

So, number of words to be learnt:
D = 4 x 20 + 70 = 150
A = 2 x 20 = 40

cheers.

thanks for the guide too

[ozora]

Hi all

I used algebra to solve this problem but is it possible to use model to solve the problem? If yes, how?
Twice of a number is greater than two-third of that number by 28.
I got the answer 21.
Thanks

[Yu Xuan]

ozora:

Hi all

I used algebra to solve this problem but is it possible to use model to solve the problem? If yes, how?
Twice of a number is greater than two-third of that number by 28.
I got the answer 21.
Thanks

Hi

Model is pretty easy to understand in this case;

Let the number be 3 units, hence twice the number will be 6 units, and 2/3 the number will be 2 units

[N][N][N][N][N][N]
[N][N]-----28 ------

4 units -->28
1 unit --> 28 ÷ 4 = 7
3 units --> 7 x 3 = 21

Yu Xuan

[lizawa]

ozora:

Hi all

I used algebra to solve this problem but is it possible to use model to solve the problem? If yes, how?
Twice of a number is greater than two-third of that number by 28.
I got the answer 21.
Thanks

Yes, it's possible to use model.

Twice of a number : draw 6 boxes
2/3 of the number : draw 2 boxes

The difference is 4 boxes (or 4u)

4u = 28
1u = 7

the number is 3u, so 3u = 3* 7 = 21.

[jieheng]

fxchow:

Hi JieHeng,

Thanks for your solution.

fxchow

Hi fxchow ,

You are welcome.

Regards,

[tianzhu]

ozora:

thanks for the guide

Hi

You're welcome.

Best wishes.