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Author Topic: IGCSE MATHS Doubts  (Read 130343 times)

Offline Ghost Of Highbury

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Re: IGCSE MATHS Doubts
« Reply #105 on: May 05, 2010, 07:05:32 pm »
Ur welcome.
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Offline Saladin

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Re: IGCSE MATHS Doubts
« Reply #106 on: May 05, 2010, 07:06:50 pm »
I think Aadi is rite in his method. dnt hav time to check exact details.
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Offline Baladya

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Re: IGCSE MATHS Doubts
« Reply #107 on: May 05, 2010, 07:19:11 pm »
Quote from: haris94 on May 05, 2010, 06:47:31 pm
V1/V2 = (l1/l2)3

so
5/v2 = (2/0.4)3
v2 = 5*(0.4)3
           (2)3

v2 = 0.04m3

0.04*1000
=40 cm3

OMG HOW DID I FORGET THE RATIO THING  ??? ??? Anyway thanks man ;)
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Offline haris94

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Re: IGCSE MATHS Doubts
« Reply #108 on: May 05, 2010, 07:24:33 pm »
lol.....no probs
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Offline The Golden Girl =D

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Re: IGCSE MATHS Doubts
« Reply #109 on: May 06, 2010, 06:03:16 am »
Quote from: contraentry on May 05, 2010, 04:30:18 pm
This is from November 1990 P4

@The golden girl: You're welcome!

You need to do the "180 - 54" because the question says it is an obtuse angle, and the Sine function proves : Sin 54 = Sin(180-54)

Moreover, 54 is not an obtuse angle, an obtuse angle is defined as an angle being greater than 90 and less than 180.

thx again !!
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Offline The Golden Girl =D

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Re: IGCSE MATHS Doubts
« Reply #110 on: May 06, 2010, 06:04:57 am »
Quote from: A@di on May 05, 2010, 04:32:48 pm
Ok if u solve it using the sine method. You get 54 degree. However they say its obtuse which means sine x = 0.809 , x =/= 54.

in such situations, u have to use the trigonometric rule sine x = sine 180-x rule  to find any other angle whose sine is 0.809

thus, 180-54 = 126. sine 126 = 0.809

Answer : 126 (Obtuse)

i didn't know that such a rule "sin =180 - 54" can come in a traingle question.....that's y i didn't even think of this rule ..........thx !!
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Offline LM

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Re: IGCSE MATHS Doubts
« Reply #111 on: May 06, 2010, 07:47:42 am »
Hey Guys...
I have billion of question I don't understand...
Could you please help me?
here are the question...

1. Carla estimates the length of the wall to be 25 m and the height to be 2 m.Paolo tells her that the length is 25 m correct to the nearest   5 m and the height is 5 m correct to the nearest 10 centimetres. Complete the statements below.
(a) ............m ? length of the wall < ...........m
(b) ............m ? height of the wall < ...........m
and everytime this kind of question come up, I never understand hooq to do it....

2.
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Offline Snake

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Re: IGCSE MATHS Doubts
« Reply #112 on: May 06, 2010, 08:23:52 am »
20M=<Length of wall<30M
1.9M=<Height of the wall<5.1M

That should be right
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Offline Dark Prince

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Re: IGCSE MATHS Doubts
« Reply #113 on: May 06, 2010, 08:46:25 am »
hey deres another Qs:

Q- Two men, John and Peter, can paint a house in 10 days. John alone can paint the house in 15 days. How long will Peter take to paint it alone?
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Offline Ghost Of Highbury

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Re: IGCSE MATHS Doubts
« Reply #114 on: May 06, 2010, 09:11:51 am »
10/15 + 10/x = 1

10x + 150
---------    =   1
     15x

10x + 150 = 15x

5x = 150

x = 150/5 = 30

30 days.

Im not sure abt this though
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Offline haris94

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Re: IGCSE MATHS Doubts
« Reply #115 on: May 06, 2010, 09:29:30 am »
can u pls explain how u got your first step:
10/15 + 10/x = 1
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Offline Vin

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Re: IGCSE MATHS Doubts
« Reply #116 on: May 06, 2010, 09:41:06 am »
Quote from: A@di on May 06, 2010, 09:11:51 am
10/15 + 10/x = 1

10x + 150
---------    =   1
     15x

10x + 150 = 15x

5x = 150

x = 150/5 = 30

30 days.

Im not sure abt this though


yup its right...i hav another method..

john n peter 10days =>   1 house
                  1 day  =>    1/10 house

john in 1 day  =>  1/15

so,  one day of john + peter =  one day of  john n peter together

1/15  +  x  =  1/10
(L.C.M)
 
1 + 15x
---------    =   1/10
   15

1  + 15x = 15/ 10

15x  =  15/10  -1
(LCM on right)

15x = 1/2

x = 1/30

peter paints 1/30 of house 1 one day...so he takes 30 days to paint one house :) :)

always try to convert any work to 1 day n solve..i find this method easy tho..dunno abt others..  :)
                   
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Offline Vin

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Re: IGCSE MATHS Doubts
« Reply #117 on: May 06, 2010, 09:44:25 am »
Quote from: haris94 on May 06, 2010, 09:29:30 am
can u pls explain how u got your first step:
10/15 + 10/x = 1

days for..(time taken for)

john+peter/john  +  john+peter/peter  =  1 house

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Offline haris94

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Re: IGCSE MATHS Doubts
« Reply #118 on: May 06, 2010, 09:53:17 am »
Quote from: ~VIN1094~ on May 06, 2010, 09:44:25 am
days for..(time taken for)

john+peter/john  +  john+peter/peter  =  1 house


hmm...yea got it Thanks
nice method By the way
 
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Offline Baladya

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Re: IGCSE MATHS Doubts
« Reply #119 on: May 06, 2010, 10:03:40 am »
This isn't only in triangles. Its also in Sine and Cosine rule. Sometimes they ask u to write the two answers for sinx under for example 180.. search google for the sine and cosine 'curve' for maths and u will understand what m saying.
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