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Percentage

by yellowho » Sun Jan 23, 2011 7:31 am
Decreasing the original price of an item by 25% and then
decreasing the new price by z% is equivalent to decreasing
the original price by

(A) 0.25(1 + 3z/100 )
(B) 0.25(1 + z/100 )
(C) 0.25(1 - 3z/100 )
(D) 0.75(1 - z/100 )
(E) 0.75(1 + 3z/100 )


Is there a way to do this without plugging?
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by yellowho » Sun Jan 23, 2011 7:46 am
oops. i don't know how to move this. jaxis, it said decreased BY so it should be 1- (.75(1-z/100). which doesn't match any of the answer. I hate these questions. Even if you know how to do it you have to find the way they do it.
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by jaxis » Sun Jan 23, 2011 7:49 am
Decreasing the original price of an item by 25% and then
decreasing the new price by z% is equivalent to decreasing
the original price by

(A) 0.25(1 + 3z/100 )
(B) 0.25(1 + z/100 )
(C) 0.25(1 - 3z/100 )
(D) 0.75(1 - z/100 )
(E) 0.75(1 + 3z/100

Let the original price be X.
First price decrease = (25/100) *X
After 25% decrease the new price is X-(25X/100) = 3X/4 = 0.75X

Now there is Z% decrease futher.

Now base price 0.75X
amont decreased = (z/100) *(0.75X)
New price = 0.75X - (z/100) *(0.75X) = X* 0.75* (1 - z/100 )

Now the question asks "equivalent to decreasing
the original price by "
So, Subtract the final amount from X(Original amount)

X- X* 0.75* (1 - z/100 ) = X(1- 0.75* (1 - z/100 )) =X(0.25+0.75*Z/100) = X*0.25 *(1+3Z/100)

I hope ive done this right.tricy wording here. Whats the OA BTW.


P.S. you have posted PS in DS section
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by jaxis » Sun Jan 23, 2011 7:51 am
yellowho wrote:oops. i don't know how to move this. jaxis, it said decreased BY so it should be 1- (.75(1-z/100). which doesn't match any of the answer. I hate these questions. Even if you know how to do it you have to find the way they do it.
Yeah Yellowho. Realized it just after posting.
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by rohu27 » Sun Jan 23, 2011 7:56 am
Let x be the original price. decreased by 25% would mean new price is 3x/4 (x-x/4)
now this is further decreased by z%:

(3x/4)-z% of 3x/4 which gives 3x/4(1-z/100)

the question asks wht percent is the resulting value of the original value x, in turn what percent of x is 3x/4(1-z/100).

3x/4(1-z/100)=x*y%. we need the value of y here.

upon solving y equals option C.
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by yellowho » Sun Jan 23, 2011 7:57 am
Yeah you are correct. I did something similar to you (see above) got stuck at .25+3z/400. I was wrong earlier. If you sub out the .25 to .25(1+3z/100). Its not easy to see that in the heat of battle. What was your instinct on this problem? Number plugging?


[quote="jaxis"][quote="yellowho"]oops. i don't know how to move this. jaxis, it said decreased BY so it should be 1- (.75(1-z/100). which doesn't match any of the answer. I hate these questions. Even if you know how to do it you have to find the way they do it.[/quote]

Yeah Yellowho. Realized it just after posting.[/quote]
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by jaxis » Sun Jan 23, 2011 8:08 am
yellowho wrote:Yeah you are correct. I did something similar to you (see above) got stuck at .25+3z/400. I was wrong earlier. If you sub out the .25 to .25(1+3z/100). Its not easy to see that in the heat of battle. What was your instinct on this problem? Number plugging?

jaxis wrote:
yellowho wrote:oops. i don't know how to move this. jaxis, it said decreased BY so it should be 1- (.75(1-z/100). which doesn't match any of the answer. I hate these questions. Even if you know how to do it you have to find the way they do it.
Yeah Yellowho. Realized it just after posting.
I woulnt recommend Plugging numbers in these type of problems.
First, u have to plug number in question.The in five options.
And if the value u chose satisfies more than one option for some reason, u have to choose another and repeat the process again.
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by hrkrishna » Sun Jan 23, 2011 8:09 am
rohu27 wrote:Let x be the original price. decreased by 25% would mean new price is 3x/4 (x-x/4)
now this is further decreased by z%:

(3x/4)-z% of 3x/4 which gives 3x/4(1-z/100)

the question asks wht percent is the resulting value of the original value x, in turn what percent of x is 3x/4(1-z/100).

3x/4(1-z/100)=x*y%. we need the value of y here.

upon solving y equals option C.
The option equal 'D'.
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by rohu27 » Sun Jan 23, 2011 8:33 am
oopss..thanks for tht. its D

hrkrishna wrote:
rohu27 wrote:Let x be the original price. decreased by 25% would mean new price is 3x/4 (x-x/4)


now this is further decreased by z%:

(3x/4)-z% of 3x/4 which gives 3x/4(1-z/100)

the question asks wht percent is the resulting value of the original value x, in turn what percent of x is 3x/4(1-z/100).

3x/4(1-z/100)=x*y%. we need the value of y here.

upon solving y equals option C.
The option equal 'D'.
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