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inversely proportional

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by manpsingh87 » Tue May 03, 2011 9:37 pm
marmar29 wrote:y varies inversly with x
a) write this statment as an equation in x , y , & k
whc is pretty easy
b)if x decreses by 20% , find the percenatege change in y ?

please shw the steps
manar
a)y=(k/x);

b) x=0.8x;
y=k/0.8x;

therefore percentage change in y= {(k/0.8x)-(k/x)}/(k/x)*100;
(0.2/0.8)*100=25%
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by marmar29 » Tue May 03, 2011 10:04 pm
many thanks :))
but i need clarification why we subtract (k / x ) from k /0.8 x ???? n why we divide by it !!??
many thanks again
manar :)
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by manpsingh87 » Tue May 03, 2011 10:12 pm
marmar29 wrote:many thanks :))
but i need clarification why we subtract (k / x ) from k /0.8 x ???? n why we divide by it !!??
many thanks again
manar :)
suppose a number say a number x which was originally 100, after a certain increase it becomes 125, then find the percentage increase of x,, how will you evaluate it..??
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by Geva@EconomistGMAT » Tue May 03, 2011 10:48 pm
marmar29 wrote:y varies inversly with x
a) write this statment as an equation in x , y , & k
whc is pretty easy
b)if x decreses by 20% , find the percenatege change in y ?

please shw the steps
manar
The "decrease by 20%" is misleading - when dealing with direct and inverse relations, ALWAYS translate the change into multiplication division:

not "decrease by 20%"

BUT rather

"Multiply times (100%-20%)=80%".

By the same token, not "Increase by 25%" but rather "multiply times (100%+25%)=125%".

This is because direct / inverse relation is an increase in ratio:

Direct relation means in simple words "expand both y and x by the same constant - whatever you multiply x, multiply y by the same constant". If you multiply x by 2, multiply y by the same 2.

Inverse relation means "whatever you multiply x, divide y by the same constant". If you multiply x by 2, DIVIDE y by the same 2. Twice the x -> half the y.
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by marmar29 » Tue May 03, 2011 11:02 pm
thanks alooot it helped me aloooooooooooot :)
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