Q&A - PSLE Math

[iFruit]

atutor2001:

pixiedust:

...Will wait for solution...

Simply :

Let the number of GROUPs of \"7 apples\" be U
Let the number of GROUPs of \"9 oranges\" be V

1 group of apple costs $4 so cost of all apples is $4U
1 group of orange costs $11 so cost of all oranges is $11V
So 4V + 11V = 999

Total number of apples is 7U (there are 7 apples in each group)
Total number of oranges is 9V (there are 9 oranges in each group)
So 7U + 9V = 1000

To find U & V we can draw model or use simultaneous.

Hi atutor2001,

Why do assume the number of apples is in groups of 7 and the number of oranges is in groups of 9? They can also be in groups and a fraction of the group, can't they?

Obviously your equations make the problem easy to solve, but is there a reason you assume the number of apples/oranges are in groups of 7/9?

[anneshirleygilbert]

tianzhu:

anneshirleygilbert:

I did it the Guess and Check method and got the answer after 10 guesses!!! Doubt students sitting in PSLE would have the luxury of time to do 10 guesses.

My answer is 343 apples and 657 oranges; but I'm curious and eager to learn your method.

Hi

Hope this helps.

First I’d like to share the thought process for this solution.

A student should be able to recognize that the number of oranges is a multiple of 9 and the number of apples is a multiple of 7.

I started with a group of 100 for ease of calculation as it’s not too difficult to get 72 oranges and 28 apples to form a group of 100 fruits.

Next multiply by 10 to get 1000 fruits.

Work in group of 63 for an increase/decrease of oranges and apples --- for balancing.

Best wishes

http://farm6.static.flickr.com/5052/5456348000_75a99120c9_b.jpg\">

Thanks, tianzhu. My GC method went very much along your line of thought. Only, I didn't think to reduce to groups of 100 which would have made calculation easier. That was a good idea. Thanks. I like your colourful illustration. Thanks for the time you took to craft it.

With the use of the calculator, I took about 9 minutes to get to arrive at the answer. Is this too long to spend on a 4 or 5 marks question in the PSLE? Pls advise.

[atutor2001]

small:

Hi atutor2001,


You are right too, I overlooked this, still have long long way to learn it. :oops:


I think normally the setter will specify the range of oranges for the question. If not, both 14 and 41 are considered correct..

Hi small

This type of question cannot use multiples because the number of girls is fixed. If multiples are to be used, we do not accept the first common number. It should be the first common number from the \"same multiple\".

If the number of girls is not fixed, e.g. packing oranges into boxes (not fixed) then we accept the first numbers that are common.

I learnt this the hard way too when teaching my kid and can still remembered it after more than 10 years.

My apology for knowingly asked the question. I feel it is the best way to understand and remember something. Actually \"questioning\" is the best way for understanding and clarity but it is also the rudest way. My apology again.

Regards

[atutor2001]

iFruit:

Hi atutor2001,

Why do assume the number of apples is in groups of 7 and the number of oranges is in groups of 9? They can also be in groups and a fraction of the group, can't they?

Obviously your equations make the problem easy to solve, but is there a reason you assume the number of apples/oranges are in groups of 7/9?

Hi iFruit

You are the real math guru here. Nothing can pass your eyes. Yes, I cheated - it is not a generic solution. Good only for primary school. The assumption that I have made it that the fruits must be sold in \"whole groups\" - which the question seems to imply.

Cheers


PS
On 2nd thought, if the groups are in fraction, then U & V will be in fraction and the equations should still be correct. So it is still a generic solution.

[stary]

iFruit:

maggilim:

Hi Please help , if possible in model method. Thanks . :?

james spend $2997 altogether on some T-shirts and Jerseys.He bought twice as many T-shirts as Jerseys. Each jersey cost $18 more than each T-shirt.He paid $351 more for the T-shirts than the Jerseys. How many Jerseys did he buy ? :?:

Let # of jerseys = []. Then # of T shirts = [][]

Then 18[] + 351 = cost of [] T shirts.

Total cost = cost of T shirts + cost of Jerseys = (18[]+351) + (18[]+351) + (18[]+351 + 18[]) = 2997

72[] + 1053 = 2997---> [] = 27



Hi all,

Get curious in this problem. Is there any simple solutions to understand?
I presume [] is the number of times or can I changed it to x.

Tks n Rgds
HTH.

[iFruit]

atutor2001:

On 2nd thought, if the groups are in fraction, then U & V will be in fraction and the equations should still be correct. So it is still a generic solution.

Hi atutor2001,

Gotcha..Thanks.

[tianzhu]

anneshirleygilbert:

With the use of the calculator, I took about 9 minutes to get to arrive at the answer. Is this too long to spend on a 4 or 5 marks question in the PSLE? Pls advise.

Hi anneshirleygilbert

I am sorry; I am not in a position to answer your question this time.

I believe the school teachers would have taught the students time management.

Your kid’s teacher would be in a better position to advise you.

Perhaps, you may find something interesting in this article.

http://www.epopular.com.sg/my-kid/100-for-maths-yes-you-can.php

Best wishes

[JSSK]

Hi,

Can anyone help with this question? Thanks.

During school open house, Pri 5 sold 55 litres of cranberry juice. The cranberry juice was sold in cups containing 200 ml & 300 ml. An equal number of cups containing 200ml & 300mil were sold. how many cups of cranberry juice did Pri 5 sell?

Regards

[pixiedust]

Hi all, I am completely :stupid: with CA1 revision.

I would greatly appreciate help with the following :

Q1:
Thanks iFruit for the solution. Yesterday there was a parents' briefing in school and it was re-iterated that algebra method, although accepted in PSLE, is not strongly encouraged. I would like to check if there are any other way to solve this problem withOUT using alegbra or ratio(not taught yet) :

Nancy has 3 times as many buttons as Mary.
Every day, Mary uses 5 buttons and Nancy uses 4 buttons.
When Mary has finished using all her buttons, Nancy has 88 buttons left.
(1) How many days does Mary take to use all her buttons ?
(2) How many buttons are there altogether at first ?


Q2:
We have the answer and solution for this question but I need the systematic way to approach such question so that if the number changes, we can still find the solution. Basically :
(a) how to find the number of pairings ?
(b) how to determine if there is a middle no partner number ? how to find it ?

10+12+14+16+.......+46+48+50=

Q3:
There were 20 questions in a test. 5 marks given for each correct answer, 2 marks deducted for each wrong answer. No mark for each blank answer. Mary scored 74 marks. How many questions did she answer correctly ?

I did it this way :
Gap --> Each wrong question, -7marks.
26 marks lost --> closest guess, 3 wrong questions hence 21 marks lost.
From here, I use G&C to find number of questions Mary answered correctly. It is easy enough due to the small numbers in the question.
Is there a more efficient way instead of G&C ?

[youngtay]

Hi, please help


Mrs Goh sells mooncakes in boxes of twos and fours. At first, there were four times as many small boxes as bog boxes. After selling half the number of small boxes and some big boxes, Mrs Goh packs 5 more boxes of mooncakes. Given that there are thrice as many small boxes as bIg boxes and there is a total of 300 mooncakes in the unsold boxes, find the number of big boxes sold. (Ans given 20 - A* maths)


TIA