Difficult PSLE 2019 Math Question!

[Pratakosong]

Source and Answer :
https://www.facebook.com/nicklebee.tutors/posts/2935987673095244

 

Edited September 27, 2019 by Pratakosong

[Ender]

This is pretty standard P6 question.

[Pratakosong]

Was sent another version of the solution on whatsapp... 

 

[Sx4falcon]

Just rearrange the shapes to become

3 joining semicircles on top + 12cm + 12cm

2 joining semicircles at the bottom + 22cm + 22cm + 16cm.

Then is obvious just minus 24cm from 60cm to get the diameter of the center semicircle.

 

 

 

[Wind30]

The answer is obvious if u just join the TOP three semi circles together. The bottom two semi circle has 10+16+10 missing which is be diameter

[Lala81]

haha honestly I'm struggling with it. 

[Lala81]

1 hour ago, Ender said:

This is pretty standard P6 question.

hmm... how do u know the distance 48?

 

[Lala81]

I understand both solutions but not ender's. Honestly if i met this in an exam, i probably couldn't answer it without preparation. Math/spatial logic not my strongest suit.

[Ody_2004]

1 minute ago, Lala81 said:

I understand both solutions but not ender's. Honestly if i met this in an exam, i probably couldn't answer it without preparation. Math/spatial logic not my strongest suit.

Yah need some thinking.. i solve by algebra.. but seem not allow or not in their syllabus 

For a twelve years old who under exam stress and time constrain maybe find it tough.. see the diagram they oredi goes.. WTF.. simi lai ei..

[Lala81]

33 minutes ago, Ody_2004 said:

Yah need some thinking.. i solve by algebra.. but seem not allow or not in their syllabus 

For a twelve years old who under exam stress and time constrain maybe find it tough.. see the diagram they oredi goes.. WTF.. simi lai ei..

yeah during math exam, i get tunnel vision, then it's GG already... Happened to me bad in A levels 

[Ender]

55 minutes ago, Lala81 said:

hmm... how do u know the distance 48?

 

When you shift the bottom two semi circle all the way to the left, you are adding 22cm on the right mah. And one more shift for the bottom right semicircle to align with the top middle semi circle will add another 4cm to the right. That is how it's 48 cm on the right. 

[Lala81]

5 minutes ago, Ender said:

When you shift the bottom two semi circle all the way to the left, you are adding 22cm on the right mah. And one more shift for the bottom right semicircle to align with the top middle semi circle will add another 4cm to the right. That is how it's 48 cm on the right. 

OH ok. Understood. But this one conceptually i think also not that straightforward also. Cos the 16-12=4 part is not easy to understand.

 

Edited September 28, 2019 by Lala81

[Ender]

1 minute ago, Lala81 said:

OH ok. Understood. But this one conceptually i think also not that straightforward also. Cos the 16-12=4 part is not easy to understand.

 

Actually this is the modelling that are taught in P4. Suppose I don't use semi circle, use blocks instead. It is exatly like shifting the blocks in a model.

[Lala81]

haha u are the math tutor for your kids. superb. Yeah i think blocks much easier to understand.

[Aloe111]

I did it by looking at half the figure since it's symmetrical.

Find the radius first.

 

[Ender]

14 minutes ago, Lala81 said:

haha u are the math tutor for your kids. superb. Yeah i think blocks much easier to understand.

Actually this particular question is not difficult for the P5 or 6 . It's the way they phrase it. Use semi circle, ask to find the diameter. Suddenly the student will be thinking whether need to use pi for calculation or not. But if they phrase it this way, shown in my picture, I am sure a P5 or even P 4  familiar with modelling will be able to solve for u. 

I guess I have worked on more Primary school assessment paper than my kids, when I saw those semi circles, using blocks to solve was natural.

 

Edited September 28, 2019 by Ender

[Lala81]

2 minutes ago, Ender said:

Actually this particular question is not difficult for the P5 or 6 . It's the way they phrase it. Use semi circle, ask to find the diameter. Suddenly the student will be thinking whether need to use pi for calculation or not. But if they phrase it this way, shown in my picture, I am sure a P5 or even P 4  familiar with modelling will be able to solve for u.

 

yeah. but some people their minds very one track one when doing math. Like me.

Hopefully don't pass down to the 2nd generation. But my girl also can see not much intrinsic ability in math 

Edited September 28, 2019 by Lala81

[Sx4falcon]

1 hour ago, Ody_2004 said:

Yah need some thinking.. i solve by algebra.. but seem not allow or not in their syllabus 

For a twelve years old who under exam stress and time constrain maybe find it tough.. see the diagram they oredi goes.. WTF.. simi lai ei..

They are allowed to use algebra if they know how to even though is not cover in their syllabus. Some tuition centre use this as 1 of their selling point during marketing.

In their syllabus, there is a topic over this type of questions.