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GMAT Official Guide Book 13th Edition Percent Help

Problem Solving — algebra and arithmetic (GMAT Focus Edition)
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by Autumnflower » Fri May 31, 2013 9:50 am
Hello guys. I am currently calculating one task on page 153 nr.8
8. When 1/10 percent of 5.000 is substracted from 1/10 of 5.000, the difference is.
a) 0
b) 50
c) 450
d) 495
e) 500

I calculated like this way: 1/10 of 5000 is 500 and when it is substracted from the same amount it is 500-500 equals 0.

When I just looked it up it says the correct answer is e).
The solution from GMAT is: Since 1/10 percent is 1/1000, the difference asked for is (1/10)(5,000)- (1/1,000)(5,000)= 500-5=495

I dont get this fraction of 1/1000.
I would apprecitae any help.

Thank you!
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by Brent@GMATPrepNow » Fri May 31, 2013 10:01 am
Autumnflower wrote:Hello guys. I am currently calculating one task on page 153 nr.8
8. When 1/10 percent of 5,000 is substracted from 1/10 of 5,000, the difference is.
a) 0
b) 50
c) 450
d) 495
e) 500
NOTE: I changed your 5.000 to 5,000 (this is the notation the GMAT uses)

You missed a key word in the question. The question says 1/10 percent of 5,000, but you calculated 1/10 of 5,000

Here's my approach.
We know that 1 percent of 5,000 equals 50 (just move the decimal 2 spaces to the left)
So, 1/10 percent of 5,000 equals 5


Next we have 1/10 of 5,000, which equals 500.

So, we get 500 - 5 = 495 = D

Cheers,
Brent
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by Autumnflower » Sat Jun 01, 2013 5:01 am
Thank you for your help!!! I got it now!
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by atikjain » Fri Jul 12, 2013 2:08 pm
Hello Everyone!!!
I have jus strtd preparing for GMAt & facing a major conceptual error (OG 13 PS Q.123)
My approach:
Mary's income = 1.6 Tim's
Juan's income = 1.4 Tim's (Tim's income 40% less than juan so juan's is 40% more than Tim)
therefor mary's income as % of juan = (1.6T/1.4T)*100 = 114%
which is not the right answer

Please help!!!!!!!!!
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by Brent@GMATPrepNow » Fri Jul 12, 2013 2:42 pm
atikjain wrote:Hello Everyone!!!
I have jus strtd preparing for GMAt & facing a major conceptual error (OG 13 PS Q.123)
My approach:
Mary's income = 1.6 Tim's
Juan's income = 1.4 Tim's (Tim's income 40% less than juan so juan's is 40% more than Tim)
therefor mary's income as % of juan = (1.6T/1.4T)*100 = 114%
which is not the right answer

Please help!!!!!!!!!
The problem is highlighted above in blue.

A lot of people make the conclusion that, if Tim's income is 40% less than Juan, then Juan's income is 40% more than Tim's.

Consider this scenario:
Tim's income = $60
Juan's income = $100
As you can see, Tim's income is 40% less than Juan's income. However, Juan's income is not 40% more than Tim's. In fact, Juan's income is 66 2/3% more than Tim's.

Here's another example that really illustrates the problem:
Tim's income = $50
Juan's income = $100
In this example, Tim's income is 50% less than Juan's income. However, Juan's income is not 50% more than Tim's. In fact, Juan's income is 100% more than Tim's.

Cheers,
Brent
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by atikjain » Fri Jul 12, 2013 5:41 pm
Thank You Brent, u saved me from a big blunder!!!!!
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by jonesk50 » Fri Oct 11, 2013 5:49 pm
Hello Brent,

So if Mary's income is $160 and Tim's income is $140, given those numbers how much did Juan make? I'm still a little confused with the question.

Please help.
Brent@GMATPrepNow wrote:
atikjain wrote:Hello Everyone!!!
I have jus strtd preparing for GMAt & facing a major conceptual error (OG 13 PS Q.123)
My approach:
Mary's income = 1.6 Tim's
Juan's income = 1.4 Tim's (Tim's income 40% less than juan so juan's is 40% more than Tim)
therefor mary's income as % of juan = (1.6T/1.4T)*100 = 114%
which is not the right answer

Please help!!!!!!!!!
The problem is highlighted above in blue.

A lot of people make the conclusion that, if Tim's income is 40% less than Juan, then Juan's income is 40% more than Tim's.

Consider this scenario:
Tim's income = $60
Juan's income = $100
As you can see, Tim's income is 40% less than Juan's income. However, Juan's income is not 40% more than Tim's. In fact, Juan's income is 66 2/3% more than Tim's.

Here's another example that really illustrates the problem:
Tim's income = $50
Juan's income = $100
In this example, Tim's income is 50% less than Juan's income. However, Juan's income is not 50% more than Tim's. In fact, Juan's income is 100% more than Tim's.

Cheers,
Brent
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by [email protected] » Sat Oct 12, 2013 12:43 pm
Hi Autumnflower,

Brent has properly explained how to solve this question in a straight-forward way, so I'm not going to rehash that.

Many GMAT questions will come with little "twists" that are meant to test how well you're paying attention. These are not tricks/traps, they're a measure of your aptitude, so you have to pay careful attention to the wording of each question. Some of the wrong answers will likely be "math mistake" answers that "catch" the people who make silly mistakes, so you might not realize you've made one. The way to protect yourself against these mistakes (and losing those points) is to take good notes and do all of your work on the pad.

GMAT assassins aren't born, they're made,
Rich
Contact Rich at [email protected]
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by Jeff@TargetTestPrep » Sun Apr 12, 2015 8:51 am
Autumnflower wrote:Hello guys. I am currently calculating one task on page 153 nr.8
8. When 1/10 percent of 5.000 is substracted from 1/10 of 5.000, the difference is.
a) 0
b) 50
c) 450
d) 495
e) 500

I calculated like this way: 1/10 of 5000 is 500 and when it is substracted from the same amount it is 500-500 equals 0.

When I just looked it up it says the correct answer is e).
The solution from GMAT is: Since 1/10 percent is 1/1000, the difference asked for is (1/10)(5,000)- (1/1,000)(5,000)= 500-5=495

I dont get this fraction of 1/1000.
I would apprecitae any help.

Thank you!
Solution:

We can break this problem into two parts:

1) What is 1/10 percent of 5,000?

2) What is 1/10 of 5,000?

Let's start with part 1.

To calculate 1/10 percent of 5,000 we must first remember to DIVIDE 1/10 BY 100.

So we have: (1/10)/(100)

To divide a number by 100 means to multiply it by 1/100, so we have:

1/10 x 1/100 = 1/1,000

Thus, 1/10 percent of 5,000 = 1/1,000 x 5,000 = 5.

(Note: If dividing 1/10 by 100 was confusing, consider a simpler example. Say we were asked for 20% of a number. Well, to get 20% as a fraction, we would divide 20 by 100. So 20% is 20/100, or 1/5.)

Now let's concentrate on part 2. We need to calculate 1/10 of 5,000. To do this we simply multiply 1/10 by 5,000.

1/10 x 5,000 = 500

The answer to part 1 is 5, and the answer to part 2 is 500. Their difference is 500 - 5 = 495.

The answer is D

Jeffrey Miller
Head of GMAT Instruction
[email protected]

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