FDP

[Videoorchard]

Hey Guys,

I have a doubt regarding the question below. The question is from the FDP Strategy guide. PG 118.

Question:
$1600 worth of $20 bills are stacked up and reach 0.35 inches high. $1050 worth of $10 bills are also stacked up.

Quantity A:
The percent by which the height of the stack of $10 bills is greater than that of the stack of $20 bills.

Quantity B:
33.5%

My Approach:
Total no of 20$ Bills: 1600/20= 80.
Total No of 10$ Bills: 1050/10=105.

The question states that 80bills(20$) occupy 0.35 inches. So the Height occupied by 105bills(10$) can be calculated by:

80->0.35inches
105->x

x=0.459 (Height occupied by 105,10$ bills)

Therefore by Intuitively you would calculate the percent by which the height of 10$ is greater than 20$ is:
0.459-0.35=0.109=10.9%.


P.S:
The above step is obviously wrong. So, Why do you make use of the forumla i.e (New-Old)/Old? When the question in quantity A, clearly asks the percent by which the height of $10 stack is "greater than" the of $20 stack . Shouldn't it be height of $10 Stack- Height of $20 Stack??

Could you please clarify by providing some example samples on when to use one approach over the another?

Thank you :)

[n00bpron00bpron00b]

Hey

I think the height is 32 inches (correct me if I am wrong)

You are right -
$1600 worth $ 20 bills => total number of notes = 80
$1050 worth $10 bills => total number of notes = 105

Height for both denominations is same (32 inches)

$ 20 bills = 80*32 = 2560
$ 10 bills = 105 * 32 = 3360

(3360-2560)/2560 = x/100
(800 x 100)/2560 = 31.25 %

Col A : 31.25%
Col B : 33.5 %

"B" greater

Regarding your doubt -

"The percent by which the height of the stack of $10 bills is greater than of the stack of $20 bills"

Notice the keywords - percent, greater than (% increase) -> the question basically is asking for the percentage increase in height between the two denominations and not just simple difference in height

Whenever there is a percent change (could be increase or decrease) we use the formula (new-old)/old = x/100 or in other words change/original = x/100.

If the question simply says by what amount is the height of $10 bills stack greater than height of $20 bills stack - then it would be simple difference 3360 - 2560 .. I doubt the test will ask such a basic question

Hope this helps

[Videoorchard]

Hi Noob,

Thank you for taking your time and helping me with your wonderful explanation! Guess,i ignored those important keywords (Percent,Increase). My bad! :D

You can also arrive at the answer from the method which i had shown earlier

80->0.35inches
105->x

x=0.459 (Height occupied by 105,10$ bills)

Percent Increase= (0.459-0.35)/0.35 = 31.14%

Therefore answer is B.

P.S:
Hey, i did check the value. Its 0.35 inches and not 35inches..(I am using the 3rd edition of strategy guide)

[n00bpron00bpron00b]

oh ! no issues :) .. actually since it says the height is same for both we can completely ignore and just calculate using the number of bills :)

[Videoorchard]

Gotcha! :)

[tommywallach]

Glad I was here to help!

(Noob, you're a king.)

-t

[n00bpron00bpron00b]

Thanks to Manhattan guides :)

[n00bpron00bpron00b]

Hi Tommy,

Not related to this thread..Is the answer to the monthly challenge problem (A) ? .. where can I find the answer for it ?

Thanks

[tommywallach]

Hey Noob,

We publish the explanation when the next post goes up, which was yesterday. So the explanation is now up!

(And yes, the answer is (A).)

-t

[n00bpron00bpron00b]

Thanks

[tommywallach]

No problem!