Question: c is What Percent of b?

Comment on c is What Percent of b?

From where did the 5/4 came from ?
gmat-admin's picture

I chose some values for b and c that satisfy the condition that b/c = 1.25 (If b = 5 and c = 4, then b/c = 5/4 = 1.25)

I could have also chosen b = 10 and c = 8, then b/c = 10/8 = 1.25

I could have also chosen b = 125 and c = 100, then b/c = 125/100 = 1.25

And so on.

Each of these pairs of values could have also been used to answer the question.

Thank you the answer and whole study material for gmat

Can't we just come from the beginning, such as :
question asks:
c is what percent of b-
c = (x/100)b
and substitute b from given stem to the above equasion b=1.25c
we will have x=100/1.25=10/0.25=10/(1/8)=80
gmat-admin's picture

Another valid approach. Nice work!

Can you tell me the level of these questions.I find it very simple.Please suggest me a good book for quant to get more than 750.
Your videos are really nice.specially the verbal section now my accuracy is increasing in verbal.
gmat-admin's picture

This question is in the 510 to 650 range.
In the Reinforcement Activities boxes under the video lessons, you'll find plenty of 700+ questions.

Alternatively, you can search GMAT Club's question database at https://gmatclub.com/forum/search.php?view=search_tags

The above link allows you to search for questions by certain topic AND by difficulty level.

please suggest reinforcement activities for this video
gmat-admin's picture

The reinforcement activities under this video https://www.gmatprepnow.com/module/gmat-arithmetic/video/1074 are nicely related to the practice question above.

Maybe a quicker way is to recognise that 1.25 relates to 0.125 = 1/8 from the conversions table ...and that it equals 10 times 1/8...which leads to 80?
gmat-admin's picture

Great idea, Anthea!

If 0.125 = 1/8, then 1.25 = 10/8 (which equals b/c)

So, "c is what percent of b?" becomes "8 is what percent of 10?"

Cheers,
Brent

ari.banerjee's picture

Hi Brent,

In the following qs;

Exactly how many bonds does Bob have?
(1) Of Bob’s bonds, exactly 21 are worth at least $5,000 each
(2) Of Bob’s bonds, exactly 65 percent are worth less than $5,000 each

How about the bonds that are bigger than 5000$?

It doesnt say that the bonds are 5000$ or less only?

In your explanation you considered exactly 5000$ and bonds that are less than 5000$. What if Bob owns bonds that are more than 5000$ as well? In that case we can not equate 36% of T to 21 or can we?

Am I missing something here?

Thank you!
gmat-admin's picture

Question link: https://gmatclub.com/forum/exactly-how-many-bonds-does-bob-have-282720.html

Great question.
The phrase AT LEAST can be rewritten as GREATER THAN OR EQUAL TO

So, if I say "All of my bowling balls weigh AT LEAST 8 pounds," then I could have bowling balls that weigh EXACTLY 8 pounds, and I could have bowling balls that weigh MORE THAN 8 pounds.

(1) Of Bob’s bonds, exactly 21 are worth at least $5,000 each
So, the values of the 21 bonds mentioned here could be: $5000, $5099, $5700, $5900, $7000, . . . etc.

(2) Of Bob’s bonds, exactly 65 percent are worth less than $5,000 each
So, the values of the bonds mentioned here could be: $4999, $4500, $3000, . . . etc.

Does that help?

Cheers,
Brent

That's an easy one.
so If b/c=1.25 ======> b/c=125/100
and the question asks about c/b which is the reciprocal of B/C mentioned above.
then, C/B must = 100/125 and by simplifying this fraction we got 20/25 and multiply by 4 nominator and denominator
we got 80/100
so the answer is 80% which is E
gmat-admin's picture

Nice work!

Hey,
I was wondering, is it possible to solve this question using the Part/Whole=Percent/100 approach? If yes, I would really appreciate it if you could kindly show me the work for this approach.
Thanks
gmat-admin's picture

You bet!

We can start by taking "c is what percent of b" and rewrite it as "c/b = x/100"

To answer this, we need to know the value of c/b

We know that b/c = 1.25,
We can convert the decimal 1.25
1.25 = 1 1/4 = 5/4

So, b/c = 5/4
This also means c/b = 4/5

We're now ready to solve the question.
We have: c/b = x/100
Substitute to get: 4/5 = x/100
Cross multiply: 5x = (4)(100)
Solve: x = 80

Answer: E

Cheers,
Brent

Hi,

I was on the right track as I found c/b = 4/5 but then I thought 4/5 = 4*1/5 and I know from the table than 1/5= 0.2 so 4/5= 0.8 therefore the answer was C. I felt very smart until I saw the answer was E. Can you tell me why my reasoning is wrong? Thank you for your this website. Having a structure to follow helps a lot! I have 5 weeks to nail 650 (cold test 460) so I'm on it!
gmat-admin's picture

You're correct to say is that 0.8 is the DECIMAL equivalent of 4/5.
However, we want the PERCENT equivalent of 4/5, which is 80%

Some examples (in the format: fraction-decimal-percent):
1/2 = 0.5 = 50%
3/4 = 0.75 = 75%
5/8 = 0.625 = 62.5%
3/5 = 0.6 = 60%

Ok, I see. I forgot the step to make it into a percent. Thank you

I think our method are the same for your video quesiton.

so b/c = 125/100, 125c = 100b, c = (100/125)b = (20/25)b

so 20*4 = 80
gmat-admin's picture

Your approach is perfect. Well done!

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