Q&A - PSLE Math

[fantasy1]

Hi



I need help for this qn :

Mr Tan is (8K + 10) yrs old.He has 2 children. Rosalind and David. Mr Tan is twice as old as Rosalind now. David is 2K years younger than Rosalynn. How old will Mr Tan be when David turns 18 yrs old ?

Thank You

[tianzhu]

Hi


You’ve also posted the same questions in the PSLE thread.

Your questions have been answered on page 826 of this thread.

http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=8250

Best wishes

[charsen]

fantasy1:

Hi



I need help for this qn :

Mr Tan is (8K + 10) yrs old.He has 2 children. Rosalind and David. Mr Tan is twice as old as Rosalind now. David is 2K years younger than Rosalynn. How old will Mr Tan be when David turns 18 yrs old ?

Thank You

Hi
Now
Tan's age--->(8k+10)
Rosalind's age---->(8k+10)/2=(4k+5)
David's age---->(4k+5)-2k=(2k+5)
Diff between Tan and David age---->(8k+10)-(2k+5)=(6k+5)

When David is 18 years old,diff between Tan and David's age will remain constant.
Hence Tan's age then, 18+(6k+5) = 6k+23

[shell]

tianzhu:

Essential:

Can help this question urgently?

Beatrice has some twenty-cent and fifty-cent coins. 2/5 of the total value of the twenty-cent coins is the same as 1/2 of the total value of the fifty-cent coins. If Beatrice spends 4 fifty-cent coins, the value of the twenty-cent coins and the value of the remaining fifty-cent coins will be the same. How many twenty-cent coins does Beatrice have? Ans 30.

Hi

Please confirm with your source.

Based on number in your question(2/5),the answer can’t be 30.

2/5 out of $6 (30 number of twenty-cent coins) is $2.40 (cannot be ½ of the total value of the fifty-cent coins).

If it is 2/3, then the answer of 30 is logical.

20 cents ----- $6 (30)

50 cents ------ $8

Best wishes

Dear Tianzhu,
This Q was found in Raffles Girls' 2012 prelim paper. I also cannot understand how to arrive at the answer. Greatly appreciate it if you can show me the steps. It would be most helpful. Cheerios, Shelby

[tianzhu]

shell:

tianzhu:

Dear Tianzhu,
This Q was found in Raffles Girls' 2012 prelim paper. I also cannot understand how to arrive at the answer. Greatly appreciate it if you can show me the steps. It would be most helpful. Cheerios, Shelby

Hi

Please help to confirm.

Is it 2/3 or 2/5?

Best wishes

[shell]

tianzhu:

shell:

[quote=\"tianzhu\"]
Dear Tianzhu,
This Q was found in Raffles Girls' 2012 prelim paper. I also cannot understand how to arrive at the answer. Greatly appreciate it if you can show me the steps. It would be most helpful. Cheerios, Shelby

Hi

Please help to confirm.

Is it 2/3 or 2/5?

Best wishes[/quote]it is 2/3

[jjxy mum]

Hi,

I need help on this question .

Cynthia walked to the library from school and at the same time, Mrs
Lee walked to school from the library. If they walked towards each other, they would meet 4 min later. If they walked in the same direction, it would take Cynthia 20 mins to catch up with Mrs Lee whose walking speed was 40 m/min. How far was the library from the school? Assume that Mrs Lee’s walking speed was constant at all times. ( Ans: 400m)

[tianzhu]

shell:

it is 2/3

Hi

Thank you for your reply.

I'll send the solution to you later.

Best wishes

[tianzhu]

jjxy mum:

Hi,

I need help on this question .

Cynthia walked to the library from school and at the same time, Mrs
Lee walked to school from the library. If they walked towards each other, they would meet 4 min later. If they walked in the same direction, it would take Cynthia 20 mins to catch up with Mrs Lee whose walking speed was 40 m/min. How far was the library from the school? Assume that Mrs Lee's walking speed was constant at all times. ( Ans: 400m)

Hi

This question has been discussed before.

As in any Speed questions, start with a simple diagram.

In 20 minutes, Mrs Lee covered 20*40 or 800 m

In 4 minutes, Mrs Lee covered 4*40 or 160 m

In 16 minutes, CYTHNIA covered 960 m (800+160)

In 4 minutes, CYTHNIA covered 240 m (960/4)

Distance between library and school ------- 400 m (240+160)

Best wishes

[tianzhu]

shell:

it is 2/3

Hi

A neat way is to use MD.

Due to time constraints, I’ll work using units.

2/3 of the total value of the twenty-cent coins is the same as 1/2 of the total value of the fifty-cent coins.

Total value of twenty-cent coins ------ 3 units

Total value of fifty-cent coins ------ 4 units

If Beatrice spends 4 fifty-cent coins, the value of the twenty-cent coins and the value of the remaining fifty-cent coins will be the same.

4 fifty-cent coins ------- $2

4 units – 2 ------ 3 units

1unit ------- 2

Total value of twenty-cent coins ------ 3 units ------ $6

Number of twenty-cent coins ------- 30 (600/20).

Another way is to use “SL” and work in a tabulated list.

20 cents: 50cents ------- 3:4 ------- 6:8

8 - 2 ------ 6, hence the condition is satisfied.

Total value of twenty-cent coins ------ 3 units ------ $6

Number of twenty-cent coins ------- 30 (600/20)

Best wishes