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Comment on c percent of c
Since ab/100=c, if we plug in
Could you please check?
How did you conclude that b =
How did you conclude that b = 10?
Hi,
Apologies. I made a silly mistake. Anyway, I really like all your videos. They are amazing.
Thank you so much.
Glad you like them!
Glad you like them!
Hi,
Is it necessary that the solution should have only numerical value or can there be variables as well?
Great question.
Great question.
If a Data Sufficiency question asks us to determine the value of some variable, we must be able to provide a single numerical value in order to conclude that the statement is sufficient.
Here's an example:
What is the value of x?
(1) 5x = 2k
If we try to solve for x, we get x = 2k/5. Since we can't provide an actual numerical value for x, statement 1 is not sufficient.
Can we write question stem
C=0.01ab and we need to find 0.01c^2 -?
from statement 1:
ab=2500/c replace in question stem c=0.01 * 2500/c and hence c^2=25 ; from here we can replace 0.01C^2= 0.01*25=0.25 - Suff
from statement 2:
a=b/c replace in question stem c=0.01*b*(b/c) , multiply both sides with c and get c^2=0.01*b^2
and we need to find:
0.01c^2=0.01*(0.01*b^2 ) - Insuf
That's a valid solution -
That's a valid solution - nice work.
Hi I have a question, would
This is a very difficult
This is a very difficult question. I'd say the difficulty level of this question is above 700. On test day, you could still get this question incorrect and still score over 750. So, don't worry about it too much. That said, be sure you understand the solution, so that it may help you with similar questions.
Fshew! Great thank you!!
Hi Brent
At 2min into the video you simplify the (AB/100 /100) to (AB/100 * 1/100) I don't understand this step?
Wouldn't it be (AB/100 * 100/1) ?
Rules of dividing by a fraction?
Cheers
To divide fractions, we
To divide fractions, we multiply by the reciprocal of the divisor.
That is, a/b ÷ c/d = a/b x d/c
Likewise, (a/b)(c/d) = a/b x d/c
First, (AB/100)/(100) is the same as (AB/100)/(100/1)
So, (AB/100)/(100) = (AB/100)/(100/1)
= (AB/100) x (1/100)
Does that help?
Yes, thank you, I was
Hi Brent,
Is this a valid approach:
Question tells us that a/100 * b = c --> ab/100=c --> ab=100c
St1) abc = 2500 --> ab =2500/c
Substitute ab with 2500/c in ab=100c --> 2500/c = 100c
Cross multiply we get 2500 = 100c^2
Divide both sides by 100 to get 25 = c^2 --> c =5 --> St1 is Suff.
St2) is not Suff.
Thanks
Aladdin
That's a perfectly valid
That's a perfectly valid solution.
Nice work!
Hi Brent,
I tried to solve it in some other way.
First I concluded that c/b = a/100, so c = ab/100.
The target question is to find c percent of c, which is c/100 = X/c, isn't it?
So, our target is to find X, which is equal to c²/100.
Using this approach, the answer is C, because we need both conditions to solve an equation.
Everything you've said is
Everything you've said is true.
The only thing is that we DON'T need both statements to determine the value of c²/100
Statement 1 says abc = 2500
IMPORTANT: On its own, statement 1 is not enough to determine the value of c²/100
However, we ALSO know that c = ab/100, which means ab = 100c
So, if we take statement 1 (abc = 2500), and replace ab with 100c, we get: (100c)c = 2500
Simplify 100c² = 2500, which means c² = 25
Now that we know c² = 25, we CAN determine the value of c²/100
c²/100 = 25/100 = 1/4
Does that help?
Cheers,
Brent
Will assigning values to a, b
The problem with testing
The problem with testing values is that strategy only yields definitive results when we get conflicting answers to the target question.
For more on this, watch the following video starting from 5:55 - https://www.gmatprepnow.com/module/gmat-data-sufficiency/video/1101
Cheers,
Brent
Hi, I did this in this way
ab=100c
abc in this ab can be replaced by 100c
100c*c=2500
c^2=25
c=5
and 5% of 5 is .25
Perfect!
Perfect!
Hi Brent,
c% of c= c/100*c= c^2/100; can i write it as c/10= ?
I have evaluated statement-1 to c = 5 or -5. Sufficient
statement-2: c=b/a; since ab=100c, substituting c value here then ab=100*b/a, by evaluating it we get a=+/-10; so insufficient.
Ans: A. Is this correct?
I'm not sure I follow your
I'm not sure I follow your logic.
You're correct to say that: c% of c = c/100*c = c^2/100
However, we can simplify this to be " What is the value of c/10 ?", since c^2/100 and c/10 are not equivalent.
Also, how did you conclude that c = 5 or -5?
Since you did arrive at the correct answer, it's quite possible your steps are mathematically sound. I'm just not following your solution.
Also, how did you conclude
a percent of b equal to c=> a/100*b=c => ab/100=c
so ab=100c; substituted the 100c in statement 1 i.e. abc=2500 then (100c)c=2500
100c^2=2500 dividing 100 on both sides=> c^2=25 => c=+/-5
Okay perfect.
Okay perfect.
Since we have two possible values of c, we need to use each value to determine the value of c percent of c (the target question).
If c = 5, then c percent of c = 5% of 5 = 0.25
If c = -5, then c percent of c = -5% of -5 = 0.25
Since we can be certain but the answer to the target question is 0.25, statement 1 is sufficient
Hi Brent, question is what is
St.1 calculation result is abc = 1/4. Not quite follow how is that answer the question? What did I miss? Thanks
Don't forget that the
Don't forget that the question has some given information.
GIVEN: a percent of b is c
In the video solution above, I used the given information to help rephrase the target question as "What is the value of abc/10,000?"
So, when statement 1 tells us that abc = 2500, we can definitely answer the REPHRASED target question (the value of abc/10,000 = 2500/10,000 = 1/4).
Here's a video lesson on rephrasing the target question: https://www.gmatprepnow.com/module/gmat-data-sufficiency/video/1100
Thanks Brent for your reply.
To clarify as C was substituted to derive abc/10,000 = 2500/10,000 = 1/4, therefore C = 1/4 ? Is my understanding correct?
No, we aren't saying that C
No, we aren't saying that C equals 1/4.
Since we rephrased the target question as "What is the value of abc/10,000?," all we are saying is that abc/10,000 = 1/4 when abc = 2500
OK think I get it now. C% of
Whoop this just show how important it is to rephrase the target question. Thanks Brent
That's exactly how we need to
That's exactly how we need to interpret those results.
Great thanks Brent for your