Q&A - PSLE Math

[tianzhu]

Verysuperkiasu:

kavisuresh:

Pls help to solve:

The fig below is made up of a circle, a triangle and two identical semicircles. The diametre of the circle is 8cm and the diametre of the semicircle is 4cm. Find the area of the shaded regions.

http://i54.tinypic.com/11vnyv8.jpg\">
thanks.

may i know anyone has the answer/sol to this?

Hi

This question from SCGS Prelim 2009 looks quite the same as the one shown in the figure.

Please see if it is useful to you.

Best wishes.

http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=1980

[cchew]

Verysuperkiasu:

kavisuresh:

Pls help to solve:

The fig below is made up of a circle, a triangle and two identical semicircles. The diametre of the circle is 8cm and the diametre of the semicircle is 4cm. Find the area of the shaded regions.

http://i54.tinypic.com/11vnyv8.jpg\">
thanks.

may i know anyone has the answer/sol to this?

The big circle + 2 semi circle - the triangle = answer

Notice that when the big circle added to the 2 semi circle, the common area between the semicircle and circle is duplicate.

[smileplease]

tianzhu:

smileplease:

Mr Samad made some toys to sell. He sold 20% of the toys on Monday. He sold 27 toys on Tuesday. On Wednesday he sold 10% of the remaining toys. After that he found that the toys he had left was 1 more than 1/2 the number of toys he had made. How many toys did he made?

Hi

Mon ------- 2 units
The remaining 8 units is subdivided into 27 (Tues) + 1 part (Wed) + 9 parts left.

8 units – 27 ------ 10 parts -------E1
5 units + 1 ------ 9 parts ------- E2

Multiply E1 by 9 and E2 by 10

72 units – 243 ------ 90 parts
50 units + 10 ------- 90 parts

22 units --------253
1 unit ------- 11.5

10 units ------ 115.

Best wishes

PS ------ The total number of 115 is a whole number which looks logical. However base on this figure, the number of toys sold on Wed is 6.5, which doesn’t seem right. Please check with the source of your question.

You are correct. BUt this is from 2010 River Valley Math prelim Paper 2 Q10.

[smileplease]

Another one Q :


Mrs Lim had twice as many ten-dollar notes as two-dollars at first. She bought a digital camera for $288 and paid for it with thrice as many two-dollar notes as ten-dollar notes. Then she realised that she had 4 times as many ten-dollar as two dollar notes left.
a) how many pieces of two-dollar notes did Mrs Lim have at first?
b) how much money had Mrs Lim left after buying the digital camera?

thank you.

[smileplease]

tianzhu, thank you very much. Your workings are always easy to understand. You are better than the school teacher.


Most of the time, my daughter’s teacher use Model method which we cannot comprehend at all.

[tianzhu]

Hi


In doing this question, students need to watch out for the difference between number of dollar notes and value of dollar notes.

As usual, I’ve drawn more MD than necessary to show the flow of events.

To all PSLE kids, wishing you the very best for your Maths paper tomorrow.

Good luck and have a good rest tonight.

Best wishes.

http://farm7.static.flickr.com/6004/6194964658_431822003d_z.jpg\">

[Verysuperkiasu]

tianzhu:

This question from SCGS Prelim 2009 looks quite the same as the one shown in the figure.

Please see if it is useful to you.

Best wishes.

http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=1980

Thank you so much, tianzhu!

[Verysuperkiasu]

cchew:

Notice that when the big circle added to the 2 semi circle, the common area between the semicircle and circle is duplicate.

Thank you for your help!

[Verysuperkiasu]

Vanilla Cake:

Q11 and answer given : 54720 cm2

http://i51.tinypic.com/34s2yw4.png\">

posted by VC's mum

if it's not too much to ask, pls help to post the above solution. My son got a very different answer.

[tianzhu]

Verysuperkiasu:

if it's not too much to ask, pls help to post the above solution. My son got a very different answer.

Hi

Design A

Area of 1 square (10*10) ------100
Area of 4 squares -------400

Area of 1 circle (r5) ------ 78.5
Area of 8 circles -------628

Shaded area ------- 1028 (400+628)

Design B

Area of big square(40*40) -------- 1600
Area of shaded area ------1600 – 1028 -----572

Difference in shaded area ------1028 – 572 ------456

6m*3.2m ------ needs 15*8 pieces of 40cm*40cm squares

More area -------456*15*8 ------ 54720.

Best wishes