Q&A - PSLE Math

[atutor2001]

tianzhu:

atutor2001:

Answer is

Half rectangle - 75

Hi atutor2001

The dimensions of the rectangle is 45 by 22.

How do you arrive at half rect ---- 75?

Please help to explain.

Triangle PVR + triangle VQS = half a rectangle.

These 2 triangles overlapped (75)

So the answer is : Half rectangle - (minus) 75

[elkniwt]

tianzhu:

Thank you for your help.


http://farm3.static.flickr.com/2547/3984945203_a6bc525a6c_o.jpg\">

Hi,

Is the answer 19:14?

If yes, this is how I got it, but I'm not sure if you can do the working this way in primary sch.

Unshaded = Area of triangle PRV + Area of triangle VSQ - overlap
= 1/2 x QR x PV + 1/2 x QR x VQ - 75
= 1/2 x 45 x 22 - 75
= 420
Shaded = Area of rect - unshaded
= 45 x 22 - 420
= 570
Hence ratio of shaded to unshaded is 570:420 = 19:14

[atutor2001]

elkniwt:

Hi,

Is the answer 19:14?

If yes, this is how I got it, but I'm not sure if you can do the working this way in primary sch.

Unshaded = Area of triangle PRV + Area of triangle VSQ - overlap
= 1/2 x QR x PV + 1/2 x QR x VQ - 75
= 1/2 x 45 x 22 - 75
= 420
Shaded = Area of rect - unshaded
= 45 x 22 - 420
= 570
Hence ratio of shaded to unshaded is 570:420 = 19:14

Correct. But you need not find the area of triangle PRV and triangle VSQ individually. They add up to \"half a rectangle\"

Unshaded = half rectangle - 75
Shaded = half rectangle + 75

[Dharma]

elkniwt:

tianzhu:

Thank you for your help.


http://farm3.static.flickr.com/2547/3984945203_a6bc525a6c_o.jpg\">

Hi,

Is the answer 19:14?

If yes, this is how I got it, but I'm not sure if you can do the working this way in primary sch.

Unshaded = Area of triangle PRV + Area of triangle VSQ - overlap
= 1/2 x QR x PV + 1/2 x QR x VQ - 75
= 1/2 x 45 x 22 - 75
= 420
Shaded = Area of rect - unshaded
= 45 x 22 - 420
= 570
Hence ratio of shaded to unshaded is 570:420 = 19:14

The unshaded area = Area of 1/2 rect - 75 = 495 - 75 = 420
Shaded area : Unshaded area = (495 + 75) : 420 = 570 : 420 = 19:14

[atutor2001]

[quote]

A man spent 1/5 of his money on clothes and a few sevenths on food. He has $152 left. How much did he spend on food?[/quote]This question is actually a prelim question from a neighbourhood school. It is very interesting because it tests the kids understanding of fractions and multiples. For those who love using model, it is the easiest way to understand.

[small]

tianzhu:

Thank you for your help.


http://farm3.static.flickr.com/2547/3984945203_a6bc525a6c_o.jpg\">

Hi Tianzhu,

Hopes this helps. I did not know if this is correct answer.

The two triangles are overlapping to each other,so we have to minus 75cm2 for one of the triangle.

http://www.postimage.org/Ts2eK_ri.jpg\">

[tianzhu]

atutor2001:

[quote]

A man spent 1/5 of his money on clothes and a few sevenths on food. He has $152 left. How much did he spend on food?

This question is actually a prelim question from a neighbourhood school. It is very interesting because it tests the kids understanding of fractions and multiples. For those who love using model, it is the easiest way to understand.[/quote]Hi
Is the answer $912?

[tianzhu]

The answer from the WS is 19:14


Best wishes

[atutor2001]

tianzhu:

quote]


Hi
Is the answer $912?

My answer is $380

[tianzhu]

atutor2001:

My answer is $380

Hi
I think you are right.
I wrongly assume the sevenths to be on the remaining sum.

Best wishes