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://greprepclub.com/forum/for-the-seven-ailments-what-is-the-median-o...

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://greprepclub.com/forum/bella-s-baubles-wants-to-sell-a-necklace-f...

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


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