Q&A - PSLE Math

[ozora]

ADoc:

LaiHeng:

[quote=\"small\"]

Hi,

HTH..


The key step is to calculate Joe's percentage. Given that Amos's salary is 20% less than Joe's.

80% of Joe = 120% of Amos
100% of Joe = 150% of Amos

Steve = 100% (10 Units)
Amos = 120% (12 Units)
Joe = 150% (15 Units)

37 Units = 2220
1 Unit = 60
12 Unit = 720

or
370% = 2220
1% = 6
120% = 720.

to anyone,
can someone enlighten how 100% of Joe = 150% of Amos?
I can't catch any clues on how to derive it.

Hi, I believe there was a typo error in the answer above.
It should be 100% of Joe = 150% of Steve instead of Amos.

Hope this clarifies.
cheers
ADoc[/quote]thanks to everyone and Adoc. It cleared my doubts.

[ozora]

another 2 new questions:

1. Every Child was accompanied by either 1 or 2 parents to a concert. If the ratio of the number of children to the number of parents is 12:17, what fraction of the children came 2 parents?

2. A bag contains 200 blue balls and 450 yellow balls. A tin contains 850 blue and 340 yellow balls. After some blue and yellow balls are moved from the tin to the bag, the percentage of the blue balls in the bag becomes 50% and the blue balls in the tin becomes 70%.
a)How many blue balls are moved from the tin to the bag?
b)How many yellow balls are moved from the tin to the bag?


thanks

[tianzhu]

Hi LaiHeng


Good Morning.

Here's the solution to Q1.

Hope this helps.

Best wishes

http://farm6.static.flickr.com/5095/5490097769_cb20f73bac_b.jpg\">

[tianzhu]

LaiHeng:

thanks .. is really clear explanation

Hi

You're welcome.

Best wishes

[tianzhu]

LaiHeng:

2. A bag contains 200 blue balls and 450 yellow balls. A tin contains 850 blue and 340 yellow balls. After some blue and yellow balls are moved from the tin to the bag, the percentage of the blue balls in the bag becomes 50% and the blue balls in the tin becomes 70%.

a)How many blue balls are moved from the tin to the bag?
b)How many yellow balls are moved from the tin to the bag?

Hi

In answering this question, a student should note that the total number of blue and yellow balls remains the same in the before and after scenarios.

Before
Bag
Blue ----- 200
Yellow ----- 450

Tin
Blue ----- 850
Yellow ----- 340

Total number of blue balls ------ 200+850 ------1050
Total number of yellow balls ------ 450+340 ------790

After
Bag
Blue ----- 1 unit
Yellow ----- 1 unit

Tin
Blue ----- 7 parts
Yellow ----- 3 parts

Here, we’ve two equations with two variables, and we cannot run away from simultaneous equations.

Some students may find it difficult to grasp SE concepts; the challenge is to help the less mathematically inclined students deal with such handicaps.

Needless to say, students who have learned SE from external courses or their parents would go ahead with SE.

Students who are able to grasp SE concepts may use letters of the alphabets to solve the equations or work using units and parts to represent the quantities of the blue and yellow balls as shown above.

Let’s begin.

1 unit + 7 parts ------1050
1 unit + 3 parts ------ 790
4 parts ------ 260

Tin
Yellow ------ 3 part ----- 3*65 ------ 195
Blue ------ 7 parts ---- 7*65 ----- 455

a)How many blue balls are moved from the tin to the bag?
850 – 455 ------ 395


b)How many yellow balls are moved from the tin to the bag?
340 – 195 ------- 145

For those students who have difficulties understanding SE, you may solve it by visualising such equations in pictorial form.

Please help to check the calculations as they had been done in a rush.

Best wishes

[ozora]

tianzhu:

Hi LaiHeng


Good Morning.

Here's the solution to Q1.

Hope this helps.

Best wishes

http://farm6.static.flickr.com/5095/5490097769_cb20f73bac_b.jpg\">

thanks
the explanation for both questions are clear. I really got a lot to learn from you.

[ozora]

tianzhu:

LaiHeng:

2. A bag contains 200 blue balls and 450 yellow balls. A tin contains 850 blue and 340 yellow balls. After some blue and yellow balls are moved from the tin to the bag, the percentage of the blue balls in the bag becomes 50% and the blue balls in the tin becomes 70%.

a)How many blue balls are moved from the tin to the bag?
b)How many yellow balls are moved from the tin to the bag?

Hi

In answering this question, a student should note that the total number of blue and yellow balls remains the same in the before and after scenarios.

Before
Bag
Blue ----- 200
Yellow ----- 450

Tin
Blue ----- 850
Yellow ----- 340

Total number of blue balls ------ 200+850 ------1050
Total number of yellow balls ------ 450+340 ------790

After
Bag
Blue ----- 1 unit
Yellow ----- 1 unit

Tin
Blue ----- 7 parts
Yellow ----- 3 parts

Here, we’ve two equations with two variables, and we cannot run away from simultaneous equations.

Some students may find it difficult to grasp SE concepts; the challenge is to help the less mathematically inclined students deal with such handicaps.

Needless to say, students who have learned SE from external courses or their parents would go ahead with SE.

Students who are able to grasp SE concepts may use letters of the alphabets to solve the equations or work using units and parts to represent the quantities of the blue and yellow balls as shown above.

Let’s begin.

1 unit + 7 parts ------1050
1 unit + 3 parts ------ 790
4 parts ------ 260

Tin
Yellow ------ 3 part ----- 3*65 ------ 195
Blue ------ 7 parts ---- 7*65 ----- 455

a)How many blue balls are moved from the tin to the bag?
850 – 455 ------ 395


b)How many yellow balls are moved from the tin to the bag?
340 – 195 ------- 145

For those students who have difficulties understanding SE, you may solve it by visualising such equations in pictorial form.

Please help to check the calculations as they had been done in a rush.

Best wishes

thanks for the prompt help.

[tianzhu]

LaiHeng:

thanks

the explanation for both questions are clear. I really got a lot to learn from you.

Hi

You're welcome.

Best wishes

[ozora]

Hi

I managed to solve this question but I wonder is there a another method.
The question is as follows: There are 80 apples and oranges in a basket. 2/5 of the oranges and 2/3 of the apples are eaten. In the end, they are 36 fruits left. How many oranges were there at first?

I used SE concepts to solve it : 2/5o+ 2/3a=44----eq1
3/50+ 1/3a=36-----eq2
I managed to get 35 oranges.

Is it possible to use model to get the answer? If so how? Thanks

[ADoc]

LaiHeng:

Hi

I managed to solve this question but I wonder is there a another method.
The question is as follows: There are 80 apples and oranges in a basket. 2/5 of the oranges and 2/3 of the apples are eaten. In the end, they are 36 fruits left. How many oranges were there at first?

I used SE concepts to solve it : 2/5o+ 2/3a=44----eq1
3/50+ 1/3a=36-----eq2
I managed to get 35 oranges.

Is it possible to use model to get the answer? If so how? Thanks

Hi! Since model is algebra (including SE) in disguise, so we can still use the so-called model method to help the students visualise this problem instead of calling it SE. So instead of using \"O\" and \"A\", we can always use the pictorial form. Also, I think students are more familiar & comfortable manipulating whole numbers compared to fractions (SE or model).

Here's a quick diagram so to speak. We can always translate to \"models\" to aid visualisation. not sure if this will be helpful. cheers!

Original
oranges [ ] [ ] [ ] [ ] [ ]
apples { } { } { }

[ ] [ ] [ ] [ ] [ ] + { } { } { } = 80 fruits
or 5 [ ] + 3 { } = 80 fruits

after eating 2/5 oranges & 2/3 apples
oranges [ ] [ ] [ ]
apples { }

[ ] [ ] [ ] + { } \t\t = 36 fruits

[ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] + { } { } { } \t= 36 x 3 = 108 fruits
|-------------9---------------| |----3-----|
or 9 [ ] + 3 { } = 108 fruits

subtracting original of 5 [ ] & 3 { }, we have:
therefore 4 [ ] = 108 - 80 = 28
1 [ ] = 7
therefore 5 [ ] = 5 x 7 = 35 oranges at first