Q&A - PSLE Math

[Rockdiva]

huh?

[Rockdiva]

oh…ok…got it…

[tisha]

Which math topic does this question test? :?

[Dharma]

Andrew Lee:

Hi ...

Annie wrote her mother's age followed by her own age to form a 4-digit number. She used the diff between their ages to subtract from the 4-digit number. Then Annie obtained the number 4489. What was Annie's age ?

Annie’s mother’s age must be 45. (Annie’s mum’s age cannot be 44 otherwise Annie will be older than her mum)

Let Annie’s age be ab

45ab – (45 – ab) = 4489
4000 + 500 + 10a + b – 40 – 5 + 10a + b = 4000 + 400 + 80 + 9
4000 + 500 + 20a + 2b = 4000 + 400 + 80 + 9 + 40 + 5
4000 + 500 + 20a + 2b = 4000 + 500 + 30 + 4
2b = 4
b = 2 or 7
If b = 2
20a = 30
a = 1.5 ( a is a whole number) – reject

If b = 7
2b = 14 (leave 4 in ones place and carry forward 10 to the tens place)
20a + 10 = 30
20a = 20
a = 1

Annie’s age = 17

[tianzhu]

Hi Dharma


Good Morning.

Wishing you a fabulous 2011.

Perhaps, another way to solve this question in an algebraic way is to consider ab as equal to a single unit

4500 + ab – (45-ab) = 4489
4455 + ab + ab =4489
ab = 34
Hence ab = 17

However for this question, it isn’t too tedious to solve it with logical reasoning and Guess and Check for students who prefer not to use algebra.

Best wishes

[tianzhu]

Belle2011:

Dear tianzhu,

Once again, thanks very much for your solution.

Cheers,
Belle.

Hi

You're welcome.

Best wishes

[INNOVATE]

tianzhu:

Hi Dharma


Good Morning.

Wishing you a fabulous 2011.

Perhaps, another way to solve this question in an algebraic way is to consider ab as equal to a single unit

4500 + ab – (45-ab) = 4489
4455 + ab + ab =4489
ab = 34
Hence ab = 17


This type of question, guess and chk method is recommended than using algebra. The latter should only be used at sec 1 level. Pupils need to come up with the ans fast under exam condition.

As it is not too complicated, the mark awarded is probably btw 2/3 marks.

However for this question, it isn’t too tedious to solve it with logical reasoning and Guess and Check for students who prefer not to use algebra.

Best wishes

[Dharma]

tianzhu:

Hi Dharma


Good Morning.

Wishing you a fabulous 2011.

Perhaps, another way to solve this question in an algebraic way is to consider ab as equal to a single unit

4500 + ab – (45-ab) = 4489
4455 + ab + ab =4489
ab = 34
Hence ab = 17

However for this question, it isn’t too tedious to solve it with logical reasoning and Guess and Check for students who prefer not to use algebra.

Best wishes

Hi Tianzhu,

Wishing you a wonderful New Year too!

Thanks for your neat and elegant solution.

[tianzhu]

Lynn2:

May I know anyone here can share where can I find very challenging questions for Circles?thanks


Rgds
Lynn

Hi

How about those questions from top schools past years papers?

They should offer sufficient practices to prepare for PSLE Maths.

Best wishes

[Rockdiva]

so can i say that the p6 qns are mostly on assumptions and logic thinking and no distinct formula to work it out?