
By: Jane Lim (offline) Wednesday, June 06 2012 @ 12:31 AM CDT (Read 3775 times)



Jane Lim 
Hi there,
Could anyone please help me with the following 2 questions.
Many thanks in advance!!

Newbie
Registered: 10/01/10 Posts: 11





By: echeewh (offline) Wednesday, June 06 2012 @ 05:34 AM CDT



echeewh 
Hello Jane,
For Q14(b), pls refer to attachment. The worked solution is on the left side (not the working /method on the right).
==========================================
Q17.
Refer to remodelled diagram in paper as per attached.
Given ODBE is a trapezium, angle ODB = 45°.
In Square Y, draw a diagonal labelled OF ( angle EOF = 45° ), where OF // DB. I.e. ODBF is a parallelogram and OF=DB=11.75cm.
In Square X, draw a diagonal labelled OG, where OG=OF=11.75cm (OG, OF are radii of semicircle with centre O). Angle FOG is a rightangled triangle (with angle FOG = 90°)
Area of Triangle FOG = (11.75 x 11.75) / 2 = (1 / 2) x Rectangle EFGH
(a)
Area (X + Y) = Area of Rectangle EFGH = 2 x Area of Triangle FOG
= 2 x [(11.75 x 11.75) / 2] = 11.75 x 11.75 = 138.06 cm2 (nearest 2 dec places)
(b)
Circumference of Semicircle = (pi / 2) x d = (pi / 2) x (11.75 x 2) = 11.75 pi
Perimeter of S,T = Circumference of Semicircle + (4 x r) , where r = radius of semicircle
= 11.75 pi + (4 x 11.75) = 83.91 cm (nearest 2 dec places)
=========================================
Trust the above helps.
Cheers,
Edward

Active Member
Registered: 04/21/11 Posts: 625





By: mlteo (online) Tuesday, June 12 2012 @ 11:19 PM CDT



mlteo 
Quote by: echeewh
(b)
Circumference of Semicircle = (pi / 2) x d = (pi / 2) x (11.75 x 2) = 11.75 pi
Perimeter of S,T = Circumference of Semicircle + (4 x r) , where r = radius of semicircle
= 11.75 pi + (4 x 11.75) = 83.91 cm (nearest 2 dec places)
=========================================
Hi Edward
Shouldn't the answer for (b) be 83.93 ?
(11.75 x pi) + (4 x 11.74) = 36.92857 + 47 = 83.92857, which rounded to 2 decimal places is
83.93.
Thanks
Regards
Teo

Newbie
Registered: 12/31/06 Posts: 10





By: echeewh (offline) Wednesday, June 13 2012 @ 03:05 AM CDT



echeewh 
Quote by: mlteoQuote by: echeewh
Hi Edward
Shouldn't the answer for (b) be 83.93 ?
(11.75 x pi) + (4 x 11.74) = 36.92857 + 47 = 83.92857, which rounded to 2 decimal places is
83.93.
Thanks
Regards
Teo
Hi Teo,
If you refer to the question, you should use the calculator's pi since question does not say to use 22/7 or 3.14.
In your case, you are using 22/7 , correct?? Your answer will be correct if the question explicitly says to use 22/7.
Hope this clarifies.
Thank you & best rgds.
Edward

Active Member
Registered: 04/21/11 Posts: 625





By: parent603 (offline) Wednesday, June 13 2012 @ 04:10 AM CDT



parent603 
Hi Edward,
Referring to Q14(b), your answer is correct. However I do not understand why the difference between the shaded and unshaded area = 4 * rectangle instead of 2 * rectangle. Pls enlighten.
Thanks for the solution.

Newbie
Registered: 11/07/11 Posts: 14





By: echeewh (offline) Wednesday, June 13 2012 @ 08:04 PM CDT



echeewh 
Quote by: parent603Hi Edward,
Referring to Q14(b), your answer is correct. However I do not understand why the difference between the shaded and unshaded area = 4 * rectangle instead of 2 * rectangle. Pls enlighten.
Thanks for the solution.
Hello parent603,
If I understand you correctly, you were asking why Shaded  Unshaded is not 2 x Rectangle. Correct??
Yes it is .. and I checked I have written in that attachment as 2 x Rectangle (3).
Did I see it wrongly or have I misinterpreted your query??
Do let me know pls. Thanks.
Kind regards,
Edward

Active Member
Registered: 04/21/11 Posts: 625





By: mlteo (online) Thursday, June 14 2012 @ 02:42 AM CDT



mlteo 
Oops. You are right, I used 22/7 as pi.
Thanks.

Newbie
Registered: 12/31/06 Posts: 10





By: parent603 (offline) Thursday, June 14 2012 @ 10:22 PM CDT



parent603 
Quote by: echeewhQuote by: parent603Hi Edward,
Referring to Q14(b), your answer is correct. However I do not understand why the difference between the shaded and unshaded area = 4 * rectangle instead of 2 * rectangle. Pls enlighten.
Thanks for the solution.
Hello parent603,
If I understand you correctly, you were asking why Shaded  Unshaded is not 2 x Rectangle. Correct??
Yes it is .. and I checked I have written in that attachment as 2 x Rectangle (3).
Did I see it wrongly or have I misinterpreted your query??
Do let me know pls. Thanks.
Kind regards,
Edward
Hello Edward,
From your attachment, there are 2 rectangles ie 1.4 * 2.5 = 2 * 1.4 * 2.5.
I am wondering why the solution is based on 4 * 1.4 * 2.5. I do understand that your soution is correct. I am curious to know why.
Thanks,

Newbie
Registered: 11/07/11 Posts: 14





By: Angch (offline) Thursday, June 21 2012 @ 09:56 AM CDT



Angch 
hi., anyone able to help problem sum Q16 ?
Thanks.

Newbie
Registered: 08/13/11 Posts: 1





By: echeewh (offline) Friday, June 22 2012 @ 12:12 AM CDT



echeewh 
Quote by: parent603Quote by: echeewhQuote by: parent603Hi Edward,
Referring to Q14(b), your answer is correct. However I do not understand why the difference between the shaded and unshaded area = 4 * rectangle instead of 2 * rectangle. Pls enlighten.
Thanks for the solution.
Hello parent603,
If I understand you correctly, you were asking why Shaded  Unshaded is not 2 x Rectangle. Correct??
Yes it is .. and I checked I have written in that attachment as 2 x Rectangle (3).
Did I see it wrongly or have I misinterpreted your query??
Do let me know pls. Thanks.
Kind regards,
Edward
Hello Edward,
From your attachment, there are 2 rectangles ie 1.4 * 2.5 = 2 * 1.4 * 2.5.
I am wondering why the solution is based on 4 * 1.4 * 2.5. I do understand that your soution is correct. I am curious to know why.
Thanks,
Hello parent603,
Sorry i missed your clarification posted here earlier.
My solution is based on:
Shaded  Unshaded = 2 x Rectangle (3)
If u see carefully , this Rectangle (3) is 2 x (given small rectangle of 2.5 x 1.4) and will have length of 2.5 and breadth of 2.8.
I believe your term 'the solution' is referring to the Answerkey, which is 4 x (small rectangle, 2.5 x 1.4)
Hence, if you were to calculate carefully, both will give you the same results.
If you still have doubts on this, pls write me an email and i will do my best to address your concerns.
Thankyou once again for clarifying..
Cheers,
Edward

Active Member
Registered: 04/21/11 Posts: 625



