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## Arithmetic Percents

tagged by: Brent@GMATPrepNow

This topic has 4 expert replies and 8 member replies
michbuk Newbie | Next Rank: 10 Posts
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1 messages

#### Arithmetic Percents

Sun Aug 26, 2012 4:30 am
Yesterday's closing prices of 2420 different stocks listed on a certain stock exchange were all different from today's closing prices. The number of stocks that closed at a higher price today than yesterday was 20% greater than the number that closed at a lower price. How many of the stocks closed at a higher price today than yesterday.
a. 484
b. 726
c. 1100
d. 1320
e. 2694

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sana.noor Legendary Member
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Wed Jan 02, 2013 10:09 am
thanks Brent

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Brent@GMATPrepNow GMAT Instructor
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Wed Jan 02, 2013 8:16 am
sana.noor wrote:
Brent Could u please lend me your mind till my gmat actual test...you are simply awesome..
here is my explanation
let "100x" be the number of stocks closed at lower price
the stocks that are closed at higher price is 20% of 100x...thus we can write that stock closed at higher price is = .2(100x)= 120X
now we can write an equation as "stock closed at lower price + stock closed at higher price = total number of stocks" = 100x +120x = 2420 = 220x = 2420 = x= 11
now we wana find the number of stocks closed at higher price, x = 11= 120x = 120(11) = 1320 answer is D..
That looks almost perfect!
The only issue is what looks to be a typo (above in green)
To calculate a 20% increase, we must take 100x and multiply it by 1.2 (not 0.2)
Your calculations are correct, I just wanted to mention this in case others were trying to follow along.

Cheers,
Brent

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sana.noor Legendary Member
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Wed Jan 02, 2013 10:09 am
thanks Brent

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### GMAT/MBA Expert

Brent@GMATPrepNow GMAT Instructor
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Wed Jan 02, 2013 8:16 am
sana.noor wrote:
Brent Could u please lend me your mind till my gmat actual test...you are simply awesome..
here is my explanation
let "100x" be the number of stocks closed at lower price
the stocks that are closed at higher price is 20% of 100x...thus we can write that stock closed at higher price is = .2(100x)= 120X
now we can write an equation as "stock closed at lower price + stock closed at higher price = total number of stocks" = 100x +120x = 2420 = 220x = 2420 = x= 11
now we wana find the number of stocks closed at higher price, x = 11= 120x = 120(11) = 1320 answer is D..
That looks almost perfect!
The only issue is what looks to be a typo (above in green)
To calculate a 20% increase, we must take 100x and multiply it by 1.2 (not 0.2)
Your calculations are correct, I just wanted to mention this in case others were trying to follow along.

Cheers,
Brent

_________________
Brent Hanneson â€“ Founder of GMATPrepNow.com
Use our video course along with

Check out the online reviews of our course
Come see all of our free resources

GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMATâ€™s FREE 60-Day Study Guide and reach your target score in 2 months!

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Matt@VeritasPrep GMAT Instructor
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Tue Jun 23, 2015 5:49 pm
michbuk wrote:
Yesterday's closing prices of 2420 different stocks listed on a certain stock exchange were all different from today's closing prices. The number of stocks that closed at a higher price today than yesterday was 20% greater than the number that closed at a lower price. How many of the stocks closed at a higher price today than yesterday.
a. 484
b. 726
c. 1100
d. 1320
e. 2694
Seems like the easiest approach is

x = # that closed higher
y = # that closed lower

x + y = 2420

and

x = 1.2y

That gives us (1.2y) + y = 2420, or y = 1100. x = 2420 - 1100, or 1320, and we're done!

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Scott@TargetTestPrep GMAT Instructor
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Tue Jun 23, 2015 3:37 pm
michbuk wrote:
Yesterday's closing prices of 2420 different stocks listed on a certain stock exchange were all different from today's closing prices. The number of stocks that closed at a higher price today than yesterday was 20% greater than the number that closed at a lower price. How many of the stocks closed at a higher price today than yesterday.
a. 484
b. 726
c. 1100
d. 1320
e. 2694
Solution:

Although this problem may seem wordy, it is actually a pretty basic word problem. We are asked to determine the number of stocks that closed at a higher price today than yesterday.

Initially, we are given that there are 2,420 different stocks. It follows that the TOTAL NUMBER of stocks is 2,420. We are also given that the number of stocks that closed at a higher price today than yesterday was 20% greater than the number that closed at a lower price. Letâ€™s define two variables and then create two equations using those variables. We can say:

H = number of stocks that closed at a higher price today than yesterday

L = number of stocks that closed at a lower price today than yesterday

With these two variables we can create two equations:

1) H + L = 2,420

2) H = 1.2L

We can now substitute 1.2L, from equation 2, for H in equation 1. So we have:

1.2L + L = 2,420

2.2L = 2,420

22L = 24,200

L = 24,200/22

L = 1,100

Since we are solving for variable H, we can plug 1,100 for L, in equation 1.

H + 1,100 = 2,420

H = 1,320

Note: Be careful of the trap in the answer choices. Notice that 1,100 was actually an answer choice. Arguably, it was put there for you to jump on, after getting 1,100 for variable L. Partial answers and answers that represent values other than the one you are being asked to find are common trap GMAT answers; donâ€™t fall for them.

Additionally, if you were running out of time and had to use a guessing strategy, there is an interesting pattern to look at as far as these answer choices go. The method Iâ€™ll describe can be used in many cases in which we are given a TOTAL value in a word problem. With this problem, we are first given that the total number of stocks in question is 2,420. If we look at our answer choices, we will find two sets of answers that, when summed, equal 2,420.

a. 484
b. 726
c. 1100
d. 1320
e. 1694

Notice that:

and

So at a bare minimum we can consider eliminating choice A because there is a slim likelihood that it is going to be the correct answer. So now we are down to 4 choices. We are also told that the number of stocks that closed at a higher price today was 20% greater than the number that closed at a lower price. This means that the value we are trying to determine, THE HIGHER PRICE, is greater than the lower price. So when we look at our two pairs of answer choices, we know the correct answer has to be the higher of the two numbers in each pair, so either 1,320 or 1,694 will be correct. Finally, we see that 1,320 is less than twice 1,110, but 1,694 is more than twice 726. However, the problem says that the higher price is only 20% greater than the lower price. Since the higher price is less than twice the lower price, the answer must be 1,320.

To be clear, the guessing tip is just that - a guessing tip. Itâ€™s far better to work a problem out in the most straightforward way possible, and leave this type of guessing for a time when you truly need it.

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gmattesttaker2 Legendary Member
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Sat Apr 20, 2013 7:35 pm
Hello,

I was trying to solve this problems as follows:

L = No. of stocks that closed at a lower price today than yesterday
H = No. of stocks that closed at a higher price today than yesterday

So, H = 1.20L

L + H = L + 1.20L = 2.20L

2.20L = 2420

So L = 1100

H = 1.20L = 1.20(1100) = 1320

OA: D

However, I still had the following questions:

1) Here we add L and H. Could there be stocks that might have closed at the same price today and yesterday?

2) "Yesterday's closing prices of 2420 different stocks listed on a certain stock exchange were all different from today's closing prices." - Do we really need this entire sentence since we are not using it anywhere? We just take 2420 out of it.

Best Regards,
Sri

sana.noor Legendary Member
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Wed Jan 02, 2013 6:08 am
Brent Could u please lend me your Brain till my gmat actual test...you are simply awesome..
here is my explanation
let "100x" be the number of stocks closed at lower price
the stocks that are closed at higher price is 20% of 100x...thus we can write that stock closed at higher price is = 1.2(100x)= 120X
now we can write an equation as "stock closed at lower price + stock closed at higher price = total number of stocks" = 100x +120x = 2420 = 220x = 2420 = x= 11
now we wana find the number of stocks closed at higher price, x = 11= 120x = 120(11) = 1320 answer is D..

_________________
Work hard in Silence, Let Success make the noise.

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Last edited by sana.noor on Wed Jan 02, 2013 10:06 am; edited 2 times in total

vijaykondepudi Newbie | Next Rank: 10 Posts
Joined
01 Jan 2010
Posted:
5 messages
Tue Jan 01, 2013 10:04 pm
Am I reading too much into the question or is it the way it's usually written ?

Definitely the language is confusing. Could some experts/Native speakers comment ..

Thank You !![/quote]

Param800 Senior | Next Rank: 100 Posts
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Tue Jan 01, 2013 2:29 pm
Sapana this the question from the OG 13. Q. 71, pg 162

Sapana wrote:
the language bugged me too.. What is the source of this question?

Sapana Senior | Next Rank: 100 Posts
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Tue Jan 01, 2013 9:45 am
the language bugged me too.. What is the source of this question?

vijaykondepudi Newbie | Next Rank: 10 Posts
Joined
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Posted:
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Sat Dec 29, 2012 9:36 pm
When I first read the question, it confused me a lot. Especially the Bold face portion in the following lines:

The number of stocks that closed at a higher price today than yesterday was 20% greater than the number that closed at a lower price. How many of the stocks closed at a higher price today than yesterday.

This mislead me to compare the number of stocks that closed higher between yesterday and today.

What does the "than yesterday" part mean ? The question is much simpler, if we omit the "than yesterday" portion.

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