Q&A - PSLE Math

[kancheongmum]

hi Dharma and James


Thank you for your explanation and I fully realize the flaw in my method. I will explain to my ds all over again and hope that he is not confused. Looking at the those questions again that use inversely proportional way of solving, yes the distance travelled is the same. Thanks really learn something from all of you.

Hi tianzhu thanks for your advice. Are you sure 2010 prelim paper are available now? Usually we have to wait till next year or Dec this year. Anyway my ds had already completed 2009 papers. He will start A* booklets and hopefully that is already enough practice. I really don’t want to stress him further as PSLE is so near.

[Dharma]

kancheongmum:

hi Dharma and James


Thank you for your explanation and I fully realize the flaw in my method. I will explain to my ds all over again and hope that he is not confused. Looking at the those questions again that use inversely proportional way of solving, yes the distance travelled is the same. Thanks really learn something from all of you.

Hi tianzhu thanks for your advice. Are you sure 2010 prelim paper are available now? Usually we have to wait till next year or Dec this year. Anyway my ds had already completed 2009 papers. He will start A* booklets and hopefully that is already enough practice. I really don't want to stress him further as PSLE is so near.

Hi kancheongmum,

Having a go at the latest 2010 Prelim papers will give your son the final practice on the latest questions before PSLE. It maybe a better practice than doing the A* booklets. Anyway, even if you do not buy the papers yourself, it is likely that his school will provide some of these papers as part of the final revision.

Good luck.

[tianzhu]

kancheongmum:

Are you sure 2010 prelim paper are available now?

Hi

As mentioned in my earlier post, 2010 P6 preliminary testpapers may be available in Sep.
You may wish to check with your usual vendors.

It's good to take a look because there may be newer trends/non routine questions.You don't have to do all the questions, just selectively do those that your kid find challenging.

Best wishes

[kancheongmum]

Hi Tianzhu and Dharma

Thanks for your advice. Hope I can get these papers for him. For his form teacher I don’t expect much cos till now the class still doing the PSLE maths booklet. My ds had completed during the June holidays with me and he was scolded for that. Sigh!!!

[tianzhu]

Hi


An interesting question from VC’s post(3rd Annual Mathlympics) regarding diagonal of square.You may wish to try to answer it using knowledge gained from Primary Maths

The diagonal of a larger square is 2 times the diagonal of a small square. Find the percentage of the small square to the bigger square.

Here’s another one.

The inner diagonal length of the square was 38 cm. Find the area of square.

Best wishes

[Maths Monster]

tianzhu:

Hi


An interesting question from VC’s post(3rd Annual Mathlympics) regarding diagonal of square.You may wish to try to answer it using knowledge gained from Primary Maths

The diagonal of a larger square is 2 times the diagonal of a small square. Find the percentage of the small square to the bigger square.

Here’s another one.

The inner diagonal length of the square was 38 cm. Find the area of square.

Best wishes

1) Small square is made up of two triangles of base u and height u/2.
Area of small square = 2 x 1/2 x u x u/2 = 1/2 x u^2

Large square is made up of two triangles of base 2u and height u.
Area of small square = 2 x 1/2 x 2u x u = 2 x u^2

Therefore, the percentage of the small square to the bigger square
= 1/2 x u^2 / (2 x u^2) x 100% = 25%

2) The inner diagonal length of the square was 38 cm.
This square is made up of two triangles of base 38cm and height 19cm.

Therefore, area of square = 2 x 1/2 x 38 x 19 = 722 cm2

[tianzhu]

Hi


Another question from VC’s post(3rd Annual Mathlympics), you may wish to solve it using heuristics learnt in primary maths.

A pest inspector killed 15 spiders and cockroaches. The number of the spiders' legs is 36 more than the number of cockroaches' legs. Find the number of cockroaches killed.

Best wishes

[Maths Monster]

tianzhu:

Hi


Another question from VC’s post(3rd Annual Mathlympics), you may wish to solve it using heuristics learnt in primary maths.

A pest inspector killed 15 spiders and cockroaches. The number of the spiders' legs is 36 more than the number of cockroaches' legs. Find the number of cockroaches killed.

Best wishes

Let number of spiders = u
Number of spiders' legs = 8u

Number of cockroaches = 15 - u
Number of cockroaches' legs = 6(15 - u)

If the number of the spiders' legs is 36 more than the number of cockroaches' legs, we can write the equation:

8u - 6(15 - u) = 36
8u - 90 + 6u = 36
14u = 126
u = 9

Therefore, number of spiders = 9 and number of cockroaches = 6

Check:
9 spiders have = 9 x 8 = 72 legs
6 cockroaches have = 6 x 6 = 36 legs
Therefore the number of the spiders' legs is 36 more than the number of cockroaches' legs

[atutor2001]

tianzhu:

Hi


Another question from VC’s post(3rd Annual Mathlympics), you may wish to solve it using heuristics learnt in primary maths.

A pest inspector killed 15 spiders and cockroaches. The number of the spiders' legs is 36 more than the number of cockroaches' legs. Find the number of cockroaches killed.

Best wishes

I remembered my kids used to do it this way.

15 x 8 = 120
120 - 36 = 84
84 / 14 = 6 cockroaches

[kancheongmum]

Hi tianzhu

I remember you have posted the solution for this question before but I can’t find it,pls help tks
Harry and Sally were at a party. Harry shook hands with 4 times as many boys as girls while Sally shook hands with 5 times as many boys as girls. How many boys and how many girls were at the party? (ans 25 boys, 6 girls)