Lesson: Finding x Percent of y

Comment on Finding x Percent of y

I'm referring to the following question:

"For the seven ailments, what is the median of the numbers of people in group 2 who have the ailments?"

My first instinct was to add up all the percents = 60. Then find the mid point ~ 30.5. Then list all the numbers in ascending order and add till I reach 30.5. Which was at (3+4+5+6+10+11) - So I calculated Median as = 11% of 400.

Can you help me think through how I was thinking about this incorrectly?


greenlight-admin's picture

Question link: http://gre.myprepclub.com/forum/for-the-seven-ailments-what-is-the-media...

Part of your approach is correct, but we need not ADD all of percents. To find the median, we list the values in ascending order, and the median is the middlemost number.

The percentages in group 2, listed in ASCENDING order are: {3%, 4%, 5%, 6%, 10%, 11%, 21%}

So, the MEDIAN value is 6%

6% of 400 = (0.06)(400) = 24

Hi Brent - for example, if the decrease from 45 to 40 is 11% does it also go the same way to say that the increase from 40 to 45 is also 11%?

greenlight-admin's picture

Great question.

The quick answer is: No, if the percent increase from X to Y is k%, then the percent decrease from Y to X is not k%.

Here's a quick example:

If we go up from 50 to 100, the percent increase is 100%

However, if we go down from 100 to 50, the percent decrease is 50%

Likewise, if we go up from 40 to 45, the percent increase = (100)(45 - 40)/40 = 500/40 = 12.5%

However, if we go down from 45 to 40, the percent increase = (100)(45 - 40)/45 = 500/45 ≈ 11.11%



Refer to this question I did it in this way
X = This week price
(60/100)*X = 179.95
X = 299.92 (Option D)

Can u pls explain why this approach is wrong
greenlight-admin's picture

Question link: https://gre.myprepclub.com/forum/bella-s-baubles-wants-to-sell-a-necklac...

If an item is 60% off (i.e., a 60% discount), then you PAY 40% of the original price.
That is: SALE price = 40% of the ORIGINAL price.

For example, if $100 = the original price, then the sale price = 0.4($100) = $40

So, in this question, the sale price = 0.4x (not 0.6x as you have in your solution).
We write: 0.4x = 179.95

Does that help?


There are 20% more goblins than wizards in magic club.
There are 120 goblins in magic club.
How many wizards are in the magic club?

Please solve.
greenlight-admin's picture

Let W = number of wizards in magic club

GIVEN: There are 20% more goblins than wizards
So, the number of goblins = (number of wizards ) + (20% more)
= W + (20% of W)
= W + 0.2W
= 1.2W

GIVEN: There are 120 goblins in magic club.
So, we can write: 1.2W = 120
Divide both sides by 1.2 to get: W = 100

Answer: 100

So, increasing a value by 20% is the same as multiplying that value by 1.2
Similarly, increasing a value by 30% is the same as multiplying that value by 1.3
And increasing a value by 78% is the same as multiplying that value by 1.78

Does that help?


Hi Brent ,
Is there any video that explains
percentage increase
percentage decrease
retail price
wholesale price
profit and loss and their percentages

greenlight-admin's picture

Hi Sri,

Here's the video on percent increase and decrease: https://www.greenlighttestprep.com/module/gre-arithmetic/video/1083

The other three concepts fall under the general heading of percents, which can be found in the above video, as well as in these two videos:
- https://www.greenlighttestprep.com/module/gre-arithmetic/video/1077
- https://www.greenlighttestprep.com/module/gre-arithmetic/video/1078


If it is assumed that 60 percent of those who receive a questionnaire by mail will respond and 300 responses are needed, what is the minimum number of questionnaires that should be mailed?

Hey Brent am i right when i say that if 60% is 300 than 100% will be x as we need total amount of questionaires
greenlight-admin's picture

Question link: https://gre.myprepclub.com/forum/if-it-is-assumed-that-60-percent-of-tho...

Sorry, but I'm not sure what you're asking. Can you provide an example?
In the meantime, I'll add a little bit more information to the solution I provided in the link.

We are told that, if x = the total number of questionnaires
Then 60% of x = the total number of responses

We want: Number of responses ≥ 300
Rewrite as: 60% of x ≥ 300
Rewrite as: 0.6x ≥ 300
Solve: x ≥ 300/0.6
Simplify: x ≥ 500

Does that help?

Oh yes thank you !!!!!

Hey Brent me again

A toy store regularly sells all stock at a discount of 20 percent to 40 percent. If an additional 25 percent were deducted from the discount price during a special sale, what would be the lowest possible price of a toy costing $16 before any discount?

i Have a confusion regarding words before any dicount shoulnt it be after discounts before means no discount
greenlight-admin's picture

Question link: https://gre.myprepclub.com/forum/a-toy-store-regularly-sells-all-stock-a...

The question, as it's presently worded ("...toy costing $16 before any discount), means that the wholesale price (the price the toy store purchased the toy) was $16

If the question were worded differently ("...what would be the lowest possible price, before any discount, of a toy costing $16), then this would be asking for the wholesale price of a toy that was offered for sale (after all discounts) at $16

Bella's Baubles wants to sell a necklace for $179.95 next week during their 60% off sale. How much should the price of the necklace be this week?

Hey Brent here i wanted to confrim than if somehting is 60% off i give 40% of price right
greenlight-admin's picture

Question link: https://gre.myprepclub.com/forum/bella-s-baubles-wants-to-sell-a-necklac...

That's correct. If the price is reduced by 60%, then the consumer pays 40% of the price.

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