Qualification > Math
IGCSE MATHS Doubts
Dibss:
--- Quote ---well i dont get this question either
A cylindrical glass has a radius of 3 centimetres and a height of 7 centimetres.
A large cylindrical jar full of water is a similar shape to the glass.
The glass can be filled with water from the jar exactly 216 times.
Work out the radius and height of the jar.
--- End quote ---
--- Quote ---Volume of glass = Pi*r2*h = 63Pi
so volume of jar = 216* 63Pi = 13608Pi cm3
since jar is similar shape to glass then ratio of height / radius of the jar = 7/3
let height of jar = h cm
h/r = 7/3
r/h = 3/7
r = 3h/7
volume of jar = Pi *(3h/7)2*h
= 9h2/49 * h * Pi
= ( 9/49)*h3* Pi
so (9/49)*h3* Pi = 13608Pi
h^3 = 13608*(49/ 9)
h = 42 => r = 42 * 3/7 = 18
r = 18 cm and h = 42 cm
--- End quote ---
there's a simpler way if you'd like actually...
(ratio of lengths)^3 = ratio of volumes
ratio of volumes = 1:216 and if you find the cube root you get ratio of sides as 1:6
then you simply multiply each length by 3 and get
r= 3x6 = 18cm
h= 7x6 = 42cm
make sense?
Dibss:
--- Quote ---then you simply multiply each length
--- End quote ---
sorry, typo... meant 6
Vin:
--- Quote from: idrees on May 08, 2010, 09:40:04 pm ---um i asked this Q .. really no one helped
can someone please explain the question
june 2007 p4 q7
--- End quote ---
Got it !! quite easy ..
a) is quite direct ..
for such kinda ques wat i always do is look for the units .. for eq in this one..
they hav asked Calculate the number of cubic metres .. 3 measurements hav to be multiplied (this is jus a tip .. this is how i under the ques)
so for this vol = 0.3 m x 1.2 x 3 m/min x 60 (for 1 hour)
= 64.8 cm3
-----------------------------------
b) same method as the previous ..
first
vol = 0.8m x 1.2m x 15 m/min x 60
= 864 cm3
for % , difference is 864 - 64.8 = 799.2
per cent = diff/original x 100
= 799.2
--------- x 100
64.8
= 1230 %
-----------------------------------
c) firstly always remember to convert ur units to units asked in ques..
1.3 mm = 0.0013m
vol = pi rrh
2 = pi r2 x 0.0013
on solvin = 22.1 m
-----------------------------------
d) take the length as L ..
surface area = 50.4/0.12
= 420 m2
SA = (0.8 x L) + (1.2 x L) + (0.8 x L)
420 = 0.8L + 1.2L + 0.8L
420 = 2.8 L
L = 150m .. done !! :)
$H00t!N& $t@r:
Hey guys do you have any notes on sine and cosine curve? If not then do you know any good site on that.
Thanks in advance!
Dibss:
do you need this for math or add math since i can't seem to remember any sine/cosine curve qs in math past papers...
do you mean sine/cosine rules by any chance?
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