Maths Paper 4 Discussion

[SmartNour]

And for the last question ( the sequence thing ) how did u guys get 0.5 and 1.5 ???

 

[Violettamee]

Yeah, i guess i messed up in the mensuration question with the truncated cone.
Didn't take the ratio but i may get some carry-forward marks, hopefully.

yeah me tooo !!!
i guess i messed up the whole darn thing !!!
omg this was bad .. just bad
please pray the curve goes down...

 

[Violettamee]

first i used the formula givin to find the area of the small cone (radius i found by cross multiplication with slanted height)
second i fund the area of full cone then i subtract the full cone with the cuted cone to get the remaining one
hope its correct

... and wt formula was that ???? the 1 u used to find the area of the small cone ?????? :\ :\ :\

 

[Violettamee]

and yeah .... there was one more question in the maths paper bout finding the frustum of the cone ...
anyone remembers?????? the questions on mensuration ...: there was this question where u needed to find the height/volume/area bla bla bla of the cone ????????? and the last question says something like this :-
this is the same cone as in part (c) with its top cut off... find the volume of the cone.." i donno it was SOMETHING like that .. u just needed to find the volume of the lower part of the cut-off cone.... :\ :\ :\

anyway any1 knows how u had to solve that ?????????????????????????

I didn't use the similarity rule here because I didn't think that's the way to do it lol. I didn't even learn the formula for a frustum thinking we won't get that.
So what I did was,

pi x radius x slant height = 108, as the dimensions of the cone was same as the cone before it.
pi x r x 15 = 108

I found radius by

108
----
15*pi

Using the value of the radius and the value of the slant height, I used Pythagora's theorem to get the perpendicular height of the cone.

In the diagram it was shown that 7.5 cm was the slant height of the cone that was cut off. 7.5 is half of 15, cut parallel to the base. This means that the cone cut off had half the dimensions of the original cone, as in slant height and perpendicular height halved.

So I repeated the procedure above with half the heigth and slant height, got the radius, and then found the volume of both cones using:
1/3 x pi x r^2 x height.

Subtracted the larger volume and the lower volume.

Wrote the answer.

damn it ... so all together i just messed up this WHOLE question :'(((((( anyway thnx Rashu ..
but then i was thinkin that in the cut-off cone .. the frustum had 2 different radii :- the one ontop was smaller than the base-radius ...... i dint know how to get THAT !!!!!!! so how do u do it ??

 

[WayneRooney10]

and yeah .... there was one more question in the maths paper bout finding the frustum of the cone ...
anyone remembers?????? the questions on mensuration ...: there was this question where u needed to find the height/volume/area bla bla bla of the cone ????????? and the last question says something like this :-
this is the same cone as in part (c) with its top cut off... find the volume of the cone.." i donno it was SOMETHING like that .. u just needed to find the volume of the lower part of the cut-off cone.... :\ :\ :\

anyway any1 knows how u had to solve that ?????????????????????????

I didn't use the similarity rule here because I didn't think that's the way to do it lol. I didn't even learn the formula for a frustum thinking we won't get that.
So what I did was,

pi x radius x slant height = 108, as the dimensions of the cone was same as the cone before it.
pi x r x 15 = 108

I found radius by

108
----
15*pi

Using the value of the radius and the value of the slant height, I used Pythagora's theorem to get the perpendicular height of the cone.

In the diagram it was shown that 7.5 cm was the slant height of the cone that was cut off. 7.5 is half of 15, cut parallel to the base. This means that the cone cut off had half the dimensions of the original cone, as in slant height and perpendicular height halved.

So I repeated the procedure above with half the heigth and slant height, got the radius, and then found the volume of both cones using:
1/3 x pi x r^2 x height.

Subtracted the larger volume and the lower volume.

Wrote the answer.

hehehehe i did the same thing

 

[Rashu712]

damn it ... so all together i just messed up this WHOLE question :'(((((( anyway thnx Rashu ..
but then i was thinkin that in the cut-off cone .. the frustum had 2 different radii :- the one ontop was smaller than the base-radius ...... i dint know how to get THAT !!!!!!! so how do u do it ??

Yes, the value of the radius will decrease. Like I explained in my earlier post, I followed the same procedure as for the first diagram to get the radius.
First, we got the slant line as 7.5 for the smaller cone and 15 cm for the larger cone. The perpendicular height for the larger cone was I think 14.8 which I found using Pythagora's theorem

Anyways I noted down the procedures here. I hope it's correct.

 

[Violettamee]

damn it ... so all together i just messed up this WHOLE question :'(((((( anyway thnx Rashu ..
but then i was thinkin that in the cut-off cone .. the frustum had 2 different radii :- the one ontop was smaller than the base-radius ...... i dint know how to get THAT !!!!!!! so how do u do it ??

Yes, the value of the radius will decrease. Like I explained in my earlier post, I followed the same procedure as for the first diagram to get the radius.
First, we got the slant line as 7.5 for the smaller cone and 15 cm for the larger cone. The perpendicular height for the larger cone was I think 14.8 which I found using Pythagora's theorem

Anyways I noted down the procedures here. I hope it's correct.

THNX SOOOOOOOOOOOOOO MUCH RASHU ... THIS WAS JUST EXTREEEEMELY HELPFUL
THNX VERY MUCH AGAIN ... :good: :good: :good: REALLY APPRECIATE IT !!!!!!! :beer: :beer:
i even saved it ... lol =D

 

[Gunner1995]

Emm this is using rounded values. I remember i used accurate UNROUNDED values and got the answer to be 71.1. Right ?

 

[Aahmsil]

Uh-huh

Emm this is using rounded values. I remember i used accurate UNROUNDED values and got the answer to be 71.1. Right ?

Yeah, I got the same.
I guess that's the correct answer

 

[majid12]

did any one feel that the exam was a bit hard?

 

[Gunner1995]

Great Real relief. Im just dissapointed at 5 lost marks for physics MC. But it was a hard paper. the A* last year was 35/40 and it was easy, so hope its like that or less.but i guess thats still an A*.. Hope i get A* in both, And everyone hear gets the grade they wish. Gotta go study for school Bio exam and Physics paper 6. Goodbye guys. Have a nice day and study well

 

[Gunner1995]

It wasnt easy. But not HARD. For instance 2002,2003 was way harder. But it wasn't that easy too... Not too low grade thresholds i assume. Probably 93 for A or something like that...

I made one silly mistake. I read 150 degrees as 105 x_x YES FACEPALM. but i guess i can forgive myself as i got the rest right.. mostly. . Gotta go now bye

 

[Aahmsil]

Weeeeee

It wasnt easy. But not HARD. For instance 2002,2003 was way harder. But it wasn't that easy too... Not too low grade thresholds i assume. Probably 93 for A or something like that...

I made one silly mistake. I read 150 degrees as 105 x_x YES FACEPALM. but i guess i can forgive myself as i got the rest right.. mostly. . Gotta go now bye

Kay bye, good luck !!!

 

[Violettamee]

did any one feel that the exam was a bit hard?

tootaaalllyy !!!!!!!!!

 

[afshinsalim]

i found it quite hard bt i managed to answer almost all the questions though i messd up the whole mensuration question

 

[Ashique]

Im really sorry to be bumping an old thread.
But for the volume
81.3/x= (15/7.5)^3
x=10.7.

 

[Ashique]

Also do you people honestly think thats we'd get only 3 marks if we have to show THATS much working as shown in the picture above? It would have been for four marks or something.

 

[OrlandoBloom<3]

Okaaay so for mensuration question the cone part ! What I did was use similarity to find the area of the smaller cone and then I simply subtracted from the bigger coneee ! I was wondering if the technique is right or not ? Thaaanks !

 

[Ashique]

^ They shaded the smaller cone, so nope not right. if they shaded the are between the small cone and the big cone then subtraction made sense.
I did this- 81.3/x= (15/7.5)^3
x=10.7.

 

[OrlandoBloom<3]

The dotted cone (above one) is similar to bigger cone which is dotted cone is inside it. Then calcuate the volume ratio between slant heights and the bring the volume of dotted cone. At end subtract the volume o dotted cone rom large cone.
This was totally indirect question.
About height it's only applying Pythagoras therom
And radius it's brought by rule o curved(lateral) area

But this person used my technique are you sureeee its wronggg ?