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## Comment on

Percent Increases and Decreases## At minute 9:16, why is 30% 0

## There are 2 ways to handle a

There are 2 ways to handle a decrease of 30%. We can find 30% of the original value and then subtract that amount from the original value, or we can just find 70% of the original value.

Here's another way to think of it. Let's say there are 100 people in a room. If 30% of those people leave, how many are remaining? Well, if 30% have left, then we know that 70% of the people are remaining. 70% of 100 = 70 people are remaining. Alternatively, 30% of 100 = 30. 100 - 30 = 70. Same answer, two ways to think of it.

## I am having a hard time

x = 300%

60 100%

x=180

Can you tell me why this doesn't work, and how to know when to use the formula?

## I believe you are confusing

I believe you are confusing "300% of" with "300% increase" and "300% more than"

300% of 50 is 150.

300% of 60 is 180.

300% of 11 is 33.

If 50 is increased by 300%, then we take 50 and add 300% of 50 to it. So, 50 increased by 300% is 200.

Likewise, 60 increased by 300% is 240.

And 11 increased by 300% is 44

On a similar note, 200 is 300% greater than 50.

And 44 is 300% greater than 11

And 4000 is 300% greater than 1000

So, in your approach, you are not treating the increase as a 300% increase. The question tells us that the new population is 300% MORE THAN the old population. However, in your approach, you are saying that the new population is 300% OF the old population. In other words, you are saying that the new population is THREE TIMES old population.

## For the question with Hilda

## You're referring to the

You're referring to the question that starts at 3:45 in the video.

The "net result" in this instance refers to the TOTAL (combined) effect of all the changes put together.

For example, if I gave you 8 apples, then took 3 apples away from you, then gave you 2 apples and then took away 1 apple, then the NET RESULT would be the same as giving you 6 apples.

In the Hilda question, increasing the wholesale price by 20% and then decreasing the resulting price by 15% has the same effect (NET RESULT) as increasing the wholesale price by 2%

Does that help?

## Dear Brent,

regarding this problem :

http://gre.myprepclub.com/forum/jack-and-jill-each-bought-the-same-tv-set-using-a-10-off-co-3534.html

can you please help me understand why adding 8.5% tax is the same as multiplying by 1.085?

and regarding this one:

http://gre.myprepclub.com/forum/qotd-21-from-2011-to-2012-jack-s-annual-salary-increased-2641.html

I think I missing here the reason why the result is expressed as that Arnie’s salary is 15.8% more than Jack’s salary, rather than that Arnie’ salary is 115.8% of Jack’s salary (what I have got). I have the feeling this may have something to do with the fact that the problem asks me “what percent greater” is Arnie’s salary compared to Jack’s salary. Am I forgetting a fundamental step? Finally, a last doubt, when a question asks me to round to the nearest 0.1%, does it simply mean that I am asked to white a percentage value rounded to the first decimal digit?

Thank you very much. I am sorry that I am writing you so many times.

## Link to the first question:

Link to the first question: http://gre.myprepclub.com/forum/jack-and-jill-each-bought-the-same-tv-se...

Why is adding 8.5% tax is the same as multiplying by 1.085?

Let x = the PRE-TAX price of the TV

So, 0.08x = the 8% tax on the TV

So, the TOTAL price = x + 0.08x = 1.08x

----------------------------------

Link to second question: http://gre.myprepclub.com/forum/qotd-21-from-2011-to-2012-jack-s-annual-...

You're correct when you say that Arnie’ salary IS 115.8% of Jack’s salary. HOWEVER, the question asks "Arnie’s salary was what percent GREATER THAN Jack’s salary?"

Other examples: "X is 116% OF Y" is the same as saying "X is 16% greater than Y"

And "X is 180% OF Y" is the same as saying "X is 80% greater than Y"

And "X is 245% OF Y" is the same as saying "X is 145% greater than Y"

------------------------------

"Finally, a last doubt, when a question asks me to round to the nearest 0.1%, does it simply mean that I am asked to white a percentage value rounded to the first decimal digit?"

That's correct!

Cheers,

Brent

## Hi Brent please I have a

## You've done everything

You've done everything correctly so far.

Using $100 for both Jack's and Arnie's 2012 salary, we get the following:

Arnie's 2011 salary = $105.263

Jack's 2011 salary = $90.909

So, we can see that Arnie's salary is $14.354 greater than Jack's salary.

The question asks "Arnie’s annual salary in 2011 was what percent greater than JACK'S annual salary in 2011?

We now know that Arnie’s 2011 salary (of $105.263) is $14.354 greater than JACK'S 2011 salary (of $90.909).

Since we're comparing the salary difference with JACK'S 2011 salary, we must take the fraction $14.354/$90.909 and convert it to a PERCENT.

We get: $14.354/$90.909 = 15.8%

Does that help?

Cheers,

Brent

## Yes it does.... thanks I

## A full glass of juice is a

(A) 1.6 ounce (B) 3.2 ounce (C) 4.8 ounce (D) 6.4 ounce (E) 8 ounces

I solved this question as below-

Given mixture : 20% Grape and 80% Apple juice

Poured in pitcher which is 200% greater than original.

Let the original volume of the mixture be x.

Now: new = (1 + 200/100)*x

new = (1+2)x

we know new which is pitcher, there was 16 ounces water added to fill the remainder of pitcher. So it can be written as original mixture x + 16. Substituting this in above equation we get-

x+16 = (1+2)x ; x+16 = 3x

16=2x x=8

So the original volume of the mixture is 8 ounces. Volume of grape juice is 20% of 8 which is 1.6 ounces. Is this method of solving correct?

## Hi Deepak,

Hi Deepak,

Your method is perfect - nice work!

Here's my full solution (it's a little different from yours): https://gre.myprepclub.com/forum/a-full-glass-of-juice-is-a-mixture-of-2...

Cheers,

Brent

## Thank you Brent, I did see it

## I have a doubt in this

From 2011 to 2012, Jack’s annual salary increased by 10 percent and Arnie’s annual salary decreased by 5 percent. If their annual salaries were equal in 2012, then Arnie’s annual salary in 2011 was what percent greater than Jack’s annual salary in 2011?

I did reach till this point where the fraction of Arnie to Jack's salary is : A/J = 1.158. Now Arnie's salary is 1.15 times Jack's salary. So it is 115.8% of Jack's salary. Which means it is 15.8% more than Jack's salary ( if we consider Jack's salary as 100) Is this understanding correct? Because I had a confusion that answer should be 115.8%.

## That's a perfectly valid

That's a perfectly valid approach, Deepak.

Cheers,

Brent

## Four feet are cut from a 12

In this question are feet and foot both same unit? If yes then answer has to be 66.66% whereas the solution is as follows-

12-8/12 *100 = 33.33%

Please suggest.

## "feet" is the plural of "foot

"feet" is the plural of "foot"

1 foot

2 feet

3 feet

However, when used in hyphen form (as in 12-foot board),we use "foot" for everything (yes, English is a lawless language!)

So, if 4 feet are removed from the 12-foot board, the board now has length 8.

Percent decrease = 100(difference in values)/ORIGINAL value

The length changes from 12 to 8 (so the original length

= 100(12 - 8)/12

= 33.333...%

Cheers,

Brent

## Thank you Brent :)

## Hello Brent,

I get a small confusion in percent change problems.When we say that the price of a pen increased by 20% ,We solve it as taking 20% of pencil's original price.(eg. original price =100$). So 20/100 *100$ = 20$. So the price of pencil increased by 20$ and new price is 100 + 20 = 120$. I understand this.

Now when in other problems like eg, Bob is 30 pounds heavier than Sara. If Bob and Sara each gain 30 pounds, then Bob's weight is 25% greater than Sara's weight. How much does Bob weigh right now?

in this question, I solved it as:

Let Bob's weight = B and sara's = S

B = S+30

Adding 30 to each of their weight:

B+30 = s+60

B+30 = 25/100 + (s+60)

This was incorrect at two places:

1) adding 30 more to sara's weight and making it s+60. Can you explain me why I'm wrong?

2) adding the percentage to Sara's weight. I added 25% to Sara's weight because I understood it as Bob is 25% greater than Sara, so adding 25% to sara's weight would be equal to Bob's weight. I added because, I get confused with the term increase and greater than. When we use the word increases,(price of a pen increases by 20%), we take 20% of pen and add the value to original value. So in the same way, should I take 25% of Sara's weight and add that value to sara's weight to get Bob's weight?

Because the expression in the solution was like:

B+30 = 1.25(S+30)

Please explain. I'm totally confused.

## If k is 25% greater than x,

If k is 25% greater than x, then we can say: k = 1.25x

Likewise, if k is 45% greater than x, then we can say: k = 1.45x

And, if k is 113% greater than x, then we can say: k = 2.13x

If k is 40% LESS than x, then we can say: k = 0.6x

Now let's examine the question...

Let B = Bob's PRESENT weight

Let S = Sara's PRESENT weight

"Bob is 30 pounds heavier than Sara."

We can write: B = S + 30 (as you have)

Adding 30 to each weight, we get:

Bob's NEW weight = B + 30

Sara's NEW weight = S + 30

ASIDE: If S = Sara's PRESENT weight, then S+30 = her NEW weight.

You said S+60 = Sara's weight, but this represents a weight gain of 60 pounds.

"Bob's weight is 25% greater than Sara's weight."

In other words: (Bob's NEW weight) = 1.25(Sarah's NEW weight)

We can write: B + 30 = 1.25(S + 30)

We now have a system of two equations:

B = S + 30

B + 30 = 1.25(S + 30)

When we solve this system, we get: S = 90 and B = 120

So, Sarah's PRESENT weight is 90 pounds, and Bob's PRESENT weight is 120 pounds

Does that help?

Cheers,

Brent

## I understand this. Thank you.

## That's correct.

That's correct.

## Hi I was doing some practice

but they don't give answers. Could you explain number 9? I get that #8 doesn't give any info on 2010 so we can't answer that but question #9 confused me.

Thanks.

## Let's say the sales for 2008

Let's say the sales for 2008 totaled $100

So, the sales for 2009 = $105 (after a 5% increase)

And the sales for 2010 = $99.75 (after a 5% decrease)

---------------------------

Question: In store D, the dollar amount of sales for 2009 was approximately what percent of the dollar amount of sales for 2010?

A) 105%

B) 106%

C) 95%

D) 104%

E) It cannot be determined from the information given.

---------------------------

We get: 105/99.75 ≈ 105/100 ≈ 105%

Answer: A

Cheers,

Brent

## Thank you. I did the same

## The percent change formula

The percent change formula will tell us the percent change from X to Y.

However, question #9 doesn't ask us to find the percent change from 2009 to 2010. Instead, we're asked the following:

The dollar amount of sales for 2009 was approximately WHAT PERCENT OF the dollar amount of sales for 2010?

In other words, we're asked "What percent of X is Y?"

So, we get: p% of X = Y (and then solve for p)

Or we can rephrase it as: "X/Y equals what percent?"

In which, we'll use: part/whole = percent/100

We get: 105/99.75 = p/100

Does that help?

Cheers,

Brent

## In what questions can we

## We can use that formula when

We can use that formula when we want to say that a certain quantity is comprised of a certain amount of one thing.

For example, if a team of 8 people is comprised of 3 males, then we can say: 3/8 = p/100

When we solve that equation for p, we'll get the percentage of the team members who are male.

Does that help?

Cheers,

Brent

## Hi, for question http://www

## Question link: http://www

Question link: http://www.urch.com/forums/gre/153587-please-help-detail-explanation.html

The word "glass" doesn't have any specific measurement associated with it.

So, we can't say that the glass must hold 8 oz of liquid.

I hope that helps.

Cheers,

Brent

## For: https://gre.myprepclub.com

## Question link: https:/

Question link: https://gre.myprepclub.com/forum/joan-bought-a-calculator-at-a-discounte...

I think you meant to say 105/0.7

Here's how I'd calculate 105/0.7 in my head"

105/0.7 = 105/(7/10)

= 105 x (10/7)

= 1050/7

= (700 + 350)/7

= 700/7 + 350/7

= 100 + 50

= 150

Cheers,

Brent

## This is highly appreciated if

Thanks

## You're referring to the

You're referring to the question that begins at 3:45 of the above video.

Let $100 - the original price

20% INCREASE

New price = (1 + 20/100)($100)

= (1 + 0.2)($100)

= (1.2)($100)

= $120

15% DECREASE

Final price = (1 - 15/100)($120)

= (1 - 0.15)($120)

= (0.85)($120)

$102

Final price = $102

Cheers,

Brent

## Yes, thank you! I knew there

## Hiya, Brent!

I am confused about one of the study questions that's related to this topic. This one: https://gre.myprepclub.com/forum/kathleen-s-weekly-salary-was-increased-by-8-percent-to-13649.html#p33761

I was able to set up the equation correctly, so I think this is more of an algebraic process question.

Here's your notes on the solution:

GIVEN: Kathleen’s weekly salary was increased by 8 percent to $237.60

We can write: x + (8% of x) = 237.60

Simplify: x + 0.08x = 237.60

Simplify: 1.08x = 237.60

Solve: x = 237.60/1.08 = 220

I am confused on how you went from this: Simplify: x + 0.08x = 237.60

To this: Simplify: 1.08x = 237.60

Specifically, where did the 1 come from? What was the step you did to simplify that?

## Question link: https:/

Question link: https://gre.myprepclub.com/forum/kathleen-s-weekly-salary-was-increased-...

Great question!

There's a bit of algebra going on here. The technique is called simplifying expressions, and it's covered later in the Algebra module here: https://www.greenlighttestprep.com/module/gre-algebra-and-equation-solvi...

Also, it's important to note that, if a term does not have a coefficient, then the coefficient is assumed to be 1.

For example, x = 1x and k² = 1k²

So, the equation: x + 0.08x = 237.60

Is the same as the equation: 1x + 0.08x = 237.60

-----------------------------

Aside: If two terms have the same variable, we can combine their coefficients. For example:

3x + 4x = 7x

8w² - 2w² = 6w²

k + k + k = 1k + 1k + 1k = 3k

----------------------------

Likewise, 1x + 0.08x = 237.60 can be simplified to 1.08x = 237.60

Does that help?

Cheers,

Brent

## Hi Again Brent,

Working through some more practice, I see another thing I don’t understand with this question: https://gre.myprepclub.com/forum/if-a-b-c-2-and-c-decreases-by-20-while-a-remains-5655.html

Here are your notes:

Given: a = b x c²

So, how about a = 2500, b = 100 and c = 5

We get: 2500 = 100 x 5²

c decreases by 20% while a remains constant

c becomes 4 and a stays at 2500

So, we get: 2500 = b x 4²

Simplify: 2500 = b x 16

Solve: 2500/16 = b

Simplify: 156.25 = b

So b INCREASES from 100 to 156.25

This represents an increase of 56.25%

Since the question asks us to round our answer to the nearest TENTH, the correct response is 56.3

What I am confused about is how reducing 5^2 by 20% gets you 4^2?

## Question link: https:/

Question link: https://gre.myprepclub.com/forum/if-a-b-c-2-and-c-decreases-by-20-while-...

Be careful. We're not decreasing 5² by 20%; we're decreasing 5 by 20%. Here's why:

In my solution, I let c = 5

The question tells us that c decreases by 20%

20% of 5 is 1.

5 - 1 = 4

So, if we decrease 5 by 20%, we get 4.

In other words, c decreases from 5 to 4

This means, c² now equals 4², which equals 16

Does that help?

## Question link: https://gre

Question link: https://gre.myprepclub.com/forum/if-a-b-c-2-and-c-decreases-by-20-while-...

For my first set of values, I used a = 2500, b = 100 and c = 5

We are then told that c decreases by 20%.

Since c = 5, we must decrease 5 by 20%

5 decreased by 20% equals 4.

Does that help?

## yup, thanks!

## Hi brent! Can you please

Wouldn't the least value of a be 4.2 and the greatest value 8.4?

In which case 2a would have be be between 4.2(2) and 8.4(2) = 8.4 and 16.8.

In which case range would be between 4.7 and 13.1

Also I dont understand the extreme values you mention...how could the smallest value of a be 8.4999 ... wouldnt that be the largest value of a?

## Solution link: https:/

Solution link: https://gre.myprepclub.com/forum/quantitative-2290.html#p4753

Sorry, I mixed up the words GREATEST and SMALLEST in my original solution. I've edited to show the proper solution.

To answer your other questions, we know that a must be greater than 4.1.

While 4.2 is greater than 4.1, there are numbers smaller than 4.2 that are still greater than 4.1.

For example, 4.11 is greater than 4.1.

Likewise, 4.10000000000000000000000000000001 is greater than 4.1

In fact, if we keep adding more zeros, a can get super close to 4.1, which is why I just used 4.1 as a possible value of a.

Conversely, we know that a is less than 8.5.

So, a could equal 8.4999999999999999999999

If we keep adding more 9's, a can get super close to 8.5, which is why I just used 8.5 as a possible value of a.

## Hey Brent i believe the links

http://gre.myprepclub.com/forum/joan-bought-a-calculator-at-a-discounted-price-that-was-30-p-3375.html

but now its this gre.my added to domain url

http://gre.myprepclub.com/forum/joan-bought-a-calculator-at-a-discounted-price-that-was-30-p-3375.html

## You're absolutely right; GRE

You're absolutely right; GRE Prep Club moved all of their contents to a different domain, but they neglected to add the necessary redirects.

My programmer is now working to change the all of the links on our site. He should be done with that in a few hours, at which point everything should be running again.

Sorry for the inconvenience!

## From 2011 to 2012, Jack’s

Hey Brent for the above question i did something but its doesnt sound logical but i got the answer can u tell me if its correct

what i did was that as in 2012 there pay was equal so i took it as 100 than applied 10% and 5% respectvly got 110 and 95 and hence by change percantage got 15.8 correct answer but in the answer exlpaintions i saw a more logical way where they took 100 same as me but than found previous pay by 100 = 1.1x and 100 = 0.95x and than did percentgae change formula

can u tell me if my appraoch was coorect or should i follow the second gre forum appraoch

please and thank you!!!!

## https://gre.myprepclub.com

Hey Brent i saw your method here and it works but can you show me if we can do it via the mulitper method please if possible?

## Question link: https://gre

Question link: https://gre.myprepclub.com/forum/gre-math-challenge-35-ms-smith-got-an-8...

By the "multiplier method," are you referring to the property that says increasing a value by 8% is the same as multiplying that value by 1.08?

If so, that strategy won't work for this question.

Why not? Because the question tells us: Ms. Smith got an 8 percent cost of living raise of $20 per week.

Here, we are given the actual dollar increase.

In other words, of the given information tells us that: 8% of Ms. Smith's old weekly salary = $20

So, if we let x = Ms. Smith's old weekly salary, then our equation becomes: 8% of x = 20, which we can solve for x.