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And for the last question ( the sequence thing ) how did u guys get 0.5 and 1.5 ???
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SonalDhanturi said: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.
haochen said: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
Rashu712 said:Violettamee said: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.
Rashu712 said:Violettamee said: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.
Violettamee said: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 ??
Rashu712 said:Violettamee said: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.
Yeah, I got the same.Gunner1995 said:Emm this is using rounded values. I remember i used accurate UNROUNDED values and got the answer to be 71.1. Right ?
Kay bye, good luck !!!Gunner1995 said: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
majid12 said:did any one feel that the exam was a bit hard?
But this person used my technique are you sureeee its wronggg ?mido4help said: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
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