Q&A - PSLE Math

[Dazzle]

Tianzhu,

Thank you so much for your answer to Q9 of MGS Prelim 2012. Will you show how to solve with Model? Thanks again.

[balu_priya]

I suggest you post this in q and a Maths.Mods please merge.

[AJH]

Hi - nd help with this question:


Mr Lee packed some oranges into big boxes and apples into small boxes. Each big box contained 50 oranges and each small box contained 30 apples. After packing, there were 12 more big boxes than small boxes. Given that there were 1240 fewer apples than oranges, how many oranges were there? ( ans: 2200 )

Thank you.

[jewelbox]

Charsen, thanks for the soln on chairs in sch halls. :thankyou:

[rsorchid]

Thanks so much.

tianzhu:

rsorchid:

Pls help, Thanks.

A florist had some roses, tulips and carnations. After selling some of them, there were 6 tulips for every 5 roses and 7 roses for every 3 carnations. After selling 168 roses, she had 456 tulips and carnations left. The number of tulips sold was the same as the number of carnations sold.
a) How many roses had she at first?
b) If the number of tulips was twice the number of carnations at first, what is the total number of tulips and carnations sold?

Hi

A neat way is to use MD.

T:R ------ 6:5 -------42:35

R:C ------ 7:3 -------- 35:15

Since the share for roses is repeated, make it the same for both set of ratios

15 + 42 ------ 57

57 units -------- 456

1 unit ------- 8

(a)Number of roses left ------- 35*8 -------- 280

Number of roses@first -------- 280+168 -------- 448

(b) Draw 1 box to show number of tulips/carnation sold.

Number of tulips left ------- 42*8 -------- 336

Number of carnations left -------- 120

1 box + 336 ------- 1 box + 120 = 1 box + 120

1 box ------- 96

The total number of tulips and carnations sold ------- 96*2 ------- 192

Best wishes

[tianzhu]

AJH:

Hi - how did u get 480? I got 460. Thank u.

Hi

This question is crafted in such a way that it’s neat to use MD.

You may also use Units and Parts or letters of the alphabet to show the variables.

What you are seeing now is already the MD.The boxes are labelled with units and parts to enable students using the UP to see better.

The number “480” refers to the number of girls.

Best wishes

[tianzhu]

Dazzle:

Tianzhu,

Thank you so much for your answer to Q9 of MGS Prelim 2012. Will you show how to solve with Model? Thanks again.

Hi

MD is one of many heuristics in the syllabus. It’s not the only way.

Sometimes, alternative way may be more appropriate.

The UP way is rather mechanical and not too difficult to pick up.

If you want to see the MD, I’ll find some time to draw and PM to you next week.

Best wishes

[tianzhu]

AJH:

Hi - nd help with this question:


Mr Lee packed some oranges into big boxes and apples into small boxes. Each big box contained 50 oranges and each small box contained 30 apples. After packing, there were 12 more big boxes than small boxes. Given that there were 1240 fewer apples than oranges, how many oranges were there? ( ans: 2200 )

Thank you.

Hi

You may use MD or work with units.

Draw three boxes (stacked up) to show the number of apples.

12*50 ------ 600

Draw five boxes to show the number of oranges. To make the MD look neater, divide 600/5 to give 120, add a bar showing 120 to each of the box.

5 boxes + 600 ------- 3 boxes + 1240

2 boxes ------- 640

1box ------ 320

Number of apples ------- 2200

Best wishes

[tianzhu]

jewelbox:

2. Chairs are arranged in rows in a sch hall. There are 6 chairs left over if 13 chairs are put in each row. Hwoever, if 15 chairs are arranged in each row, there will be a shortage of 4 chairs. if the no. of people attending the concert is betw 200 and 30, find the no. of chairs in the hall.

Hi

Use “SL” to get the answer of 266.

Do a tabulated list of multiples of 13 + 6 and multiples of 15 – 4.

Or alternatively find the multiples of 13 and 15 which give a difference of 10.

Then find multiple of 13 + 6 or multiple of 15 – 4.

Best wishes

[tianzhu]

ximinful:

Hi,can someone help me with nanyang 2012 prelim q10?

Hi

If you’re referring to the Speed question, I’ll try to do some sketch and PM to you early next week.

Best wishes