Q&A - PSLE Math

[kancheongmum]

starlight1968sg:

Dreamybee:

Pls kindly help-Tks alot


The ratio of $2 notes to $5 notes in Joan's piggy bank was 13:8. She exchanged 20pieces of $2 notes for some $5 notes, after which, the ratio of $2 notes to $5 notes became 4:5. What was the total value if $2 notes and $5 notes in the piggy bank at first?

What is the ans?
I got 52 pieces of $2 and 32 pieces of $5.
So total value is $264.

Hi dreamybee I have another method
since this is internal transfer, I will change the quantity ratio into value ratio so that we get unchange total in value.

13:8 ---- 26:40 --- 13:20 (at first) total 33U
4:5 ---- 8:25 (after) total 33U

there is a transfer of 5U from $2 t $5

5U --- 20 x $2 = $40
1U --- $8

No. of $2 notes at first ($8x13) / $2 =52
No. of $5 notes at first ($8x20)/$5= 32

total value (52 x$2) + (32x$5)= $264

[Dreamybee]

Tks alot…


But I guess my Maths is really bad…Still catch no ball…

Sigh…Been stressing over the top school Maths so much these days…

[Dharma]

Dreamybee:

Pls kindly help-Tks alot


The ratio of $2 notes to $5 notes in Joan's piggy bank was 13:8. She exchanged 20pieces of $2 notes for some $5 notes, after which, the ratio of $2 notes to $5 notes became 4:5. What was the total value if $2 notes and $5 notes in the piggy bank at first?

Value of $2 notes at first = 13u x $2 = $26u
Value of $5 notes at first = 8u x $5 = $40u

20 pieces of $2 notes = $40

Value of $2 notes at last = 4p x $2 = $8p
Value of $5 notes at last = 5p x $5 = $25p

$26u - $40 =$8p ..........(1)
$40u + $40 = $25p ......(2)

Multiply (1) by 25 and (2) by 8 and equating them

$650u - $1000 = $3200u + $320
$330u = $1320
1u = 4

Total value of $2 notes and $5 notes at first
= $66u
= $66 x 4
= $264

[tianzhu]

Hi Dreamybee


This question touches on before and after scenarios involving two changed quantities. The quantities (the number of notes) at the beginning and the end are different.

I know of three ways to tackle this question. They are Units and Parts (UP), MD and Systematic Listing. I think UP is an efficient way solve such problem. It’s also my boy’s favourite when he was doing PSLE Maths. I am not sure why, but he simply loves it. If you get more familiar with UP, you’ll realise that it is applicable to a wide spectrums of questions.

I’ll try to guide you through the steps with the following slides.Hope this helps.

Best wishes

PS ---Another way to look at this question is to use the values of the notes rather than their numbers. Please refer to Dharma and kancheongmum's solutions


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[Dreamybee]

Tks alot everyone ESP Tianzhu! I got it…


Juz when everyone was telling me time is short n I am almost on the verge of giving up, I find encouragement n warmth here… I had been trying means n ways to help my twins to find best solving methods…tks alot!!!

Here is another question- pls help if u can…

60% of the people at a water theme park were adults. 75% of the remainder were boys. There were 140 more adults than girls. More children came to the park, after which 60% of the people in the park were children. How many more children came to the park? (Ans : 140 more)

[ksmama]

Dreamybee:

Tks alot everyone ESP Tianzhu! I got it...


Juz when everyone was telling me time is short n I am almost on the verge of giving up, I find encouragement n warmth here.. I had been trying means n ways to help my twins to find best solving methods..tks alot!!!!

Here is another question- pls help if u can..

60% of the people at a water theme park were adults. 75% of the remainder were boys. There were 140 more adults than girls. More children came to the park, after which 60% of the people in the park were children. How many more children came to the park? (Ans : 140 more)

Hi tianzhu/mathsmonster for all your tireless contributions.
1 method for the above

adults : kids
6 : 4

adults : boys : girls
6 : 3 : 1 ( since 3/4 of remainder were boys)

no. of adults 140 more than girls
therefore 6-1 = 5 units = 140
1 unit = 28
adults is 6u=6x28=168
kids= 4u =4x28=112

We were told some kids joined in and the ratio became
adults : kids
4 : 6
to simplify2 : 3
but we know that the no. of adults remained unchanged.
Therefore the 2 parts in the end is equal to 168 as well
1 part = 84
since no. of kids is 3 parts = 3 x 84 =252
so no. of children that came to the park = 252-112=140

[kancheongmum]

Dreamybee:

Tks alot everyone ESP Tianzhu! I got it...


Juz when everyone was telling me time is short n I am almost on the verge of giving up, I find encouragement n warmth here.. I had been trying means n ways to help my twins to find best solving methods..tks alot!!!!

Here is another question- pls help if u can..

60% of the people at a water theme park were adults. 75% of the remainder were boys. There were 140 more adults than girls. More children came to the park, after which 60% of the people in the park were children. How many more children came to the park? (Ans : 140 more)

hi dreamybee don't give up, your twins still have a long way to go. Their learning journey don't end at PSLE. I really pity the children. They have to remember so much things. Come to think of it, we can't even do some of the things they are doing now. Just to encourage you, my youngest son is also so, so comparing to his 3 older siblings. They are so self-motivated that I don't have to do any work with them. I just send them to tuition centre and let the tutor do the work. Of course spend a lot of money on tuition. Their results are very good by my standard which means they can go to prestige sec school. I thought the formula will work for my youngest until I found out he is writing a one sentence composition, no paragraphs, commas all the way and one full stop in the end in P4. Tuition centre doesn't work for him. So get private tutor just for English and I handle Science and Maths. I am very upset and even blame myself for not teaching and guiding him from the start and it is too late. Well it is never too late because they are your children. I have a very good friend whose 2 sons grew up together with mine. They went to the same tuition centre and pri school. Both in N level in sec school. She did not even get upset or compare with my children. So I have a long chat with her and she really open up my vision. Just guide him along and the rest is up to him. I am mentally prepared for my ds to go N level. For me the most important thing is pray that he will get a good teacher that can encourage and motivate him which the sons of my good friend had. They both doing very well now in poly. I hope this can encourage you. As for your maths questions, someone has already post the solution. Let us know if you can't understand.
All the best and enjoy learning and guiding your twins. Someone told me this long time ago, tough time will pass but tough person will always stay.

[tianzhu]

Dreamybee:

Juz when everyone was telling me time is short n I am almost on the verge of giving up, I find encouragement n warmth here.. I had been trying means n ways to help my twins to find best solving methods..tks alot!!!!

Hi

Do not waste precious resources searching for the best solving methods, to get the right answer; all you really need is a good solution.

Give your twins the opportunity to look at different ways of arriving at a solution, let them decide what is the better approach for them to take.

Do it the KS way.

Keep (in) Syllabus.
Keep (it) Short.
Keep (it) Simple.

Keep Supporting your kids, enjoy the PSLE journey.

Best wishes

[Dreamybee]

Thanks to everyone for yr kind words n support…


I am nt aiming for A* or wat for my twins… It’s juz tat I dun wish tat Maths will pull dwn their Maths as they r doing fine for rest of subjects…

I need easy to understand solutions as I must understand n teach them…

I am motivated now… No words could describe hw thankful I am to everyone here…

THANK YOU n PLS CONTINUE TO HELP!!!

[James Ang]

Came across some thinking type questions in sec 1 textbooks that can be solved using model/primary methods.;


1. Jack cycles to his friend’s house and then returns home by the same route. He always cycles at 4 km/h when going uphill and, 12 km/h when going downhill, and 6 km/h when on level ground. If his total cycling time is 2h 20mins, what is the distance he cycles in km?


2. Two candles of the same height are lit at the same time. The first candle takes 5h to burn completely. The second candle takes 4h to burn completely. If each candle burns at a constant rate, how long does it take, in hours, for the height of the first candle to be four times that of the second candle?