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Comment on Find the Ratio a:b:c
in regards to statement 1.
Once we know that the a:b:c
Once we know that the a:b:c ratio is equal to c/3 : c/2 : c, we can create an equivalent ratio that eliminates the fractions. We create that equivalent ratio by multiplying all three values by 6 (the least common multiple of 2 and 3) to get 2c : 3c : 6c
This is no different than taking the ratio 1 : 2 and multiplying both values by 5 to get the equivalent ratio 5 : 10
Does that help?
i don't understand the second
and how can i say insufficient
For statement 2, we're told
For statement 2, we're told that c = 6 AND ab = c
In other words, ab = 6
So, when we test certain values of a, b and c, those values must meet the given conditions.
NOTE: The values I used are not the only values meet the given conditions. We COULD have used other values. Here are some examples:
a = 1, b = 6, c = 6 (a:b:c = 1:6:6)
a = 0.5, b = 12, c = 6 (a:b:c = 0.5:12:6)
a = 4, b = 1.5, c = 6 (a:b:c = 4:1.5:6)
a = 3, b = 2, c = 6 (a:b:c = 3:2:6)
Notice that the ratio a:b:c is different each time. So, using the information in statement 2, we cannot answer the target question with certainty.
Does that help?
What is the target question
The target question for both
The target question for both statements is "What is the ratio a:b:c?
Thank you gmat-admin, your
That's correct.
That's correct.
for statement 1, you can also
The ratios 2:3:6 and 4:6:12
The ratios 2:3:6 and 4:6:12 are equivalent. So, there is still only one answer to the target question.
For 1), How do we know c is
For statement 1, we are
For statement 1, we are trying to rewrite the variable in terms of c.
So, for example, we rewrote a as a = c/3
Likewise, we rewrote b as b = c/2
Now comes c. What do we do with that? Well, since our goal is to rewrite each variable in terms of c, we can see that c is ALREADY written in terms of c. That is, c = c.
So, we're done!
Does that help?
I can't believe I got this
That's great to hear! Thanks
That's great to hear! Thanks for saying that.
Hi,
why doesn't this method work?
c/a = 3/1 (cross multiply) to get 3a = C ie, ratio of 3;1???
thanks
What relationship do you feel
What relationship do you feel has a ratio of 3:1?
If you feel that, since 3a = c, then the ratio a:c = 3:1, this is not correct.
We can verify this by examining some values of a and c that satisfy the equation 3a = c
One such solution is a = 1 and c = 3, in which case a : c = 1 : 3
Another such solution is a = 2 and c = 6, in which case a : c = 2 : 6 = 1 : 3
Etc
Does that help?
Hi Brent,
Is this solution for the question in the video correct, my concern is Statement1 only:
Statement1:
c/a = 3, --> c:a =3:1
c/b=2 --> c:b = 2:1
c is the common, so let's make it equal in both rations
multiply by 2, c:a = 6:2 and c:b = 6:3
so a : b : c = 2 : 3: : 6
Statement 1 is Suff.
Statement 2 is not Suff.
Thanks
Aladdin
That's a perfect solution,
That's a perfect solution, Aladdin!
Is there anything wrong with
C/A = 3/1 and C/B = 2/1 so you have C:A 3:1 and C:B 2:1 convert to common C and get C:A = 6:2 C:B = 6:3 so your ratio is 2:3:6.
I guess my question is, am i wrong in assuming in the original that:
C = 3 and C = 2
A = 1 and B = 1
Does that make sense?
That approach totally works
That approach totally works with this question.
The only thing I'd add is that, if C/A = 3/1, then it's quite possible that C = 3 and A = 1.
So, using those values in your solution will yield the correct answer.
That said, if C/A = 3/1, then it's ALSO quite possible that C = 6 and A = 2.
So, using those values in your solution will ALSO yield the correct answer (as will C = 12 and A = 4, etc)
Cheers,
Brent
hi Brent,
Could you help me with the below question?
The monthly savings of a person is two fifths of his monthly salary. If his monthly salary is increased by 7/13th and his expenditure remains unchanged, then what will be ratio of new savings to old savings?
Let M = ORIGINAL monthly
Let M = ORIGINAL monthly salary.
Since he saves 2/5 of his salary, the amount saved = 2/5 of M
= 2M/5
ASIDE: this also tells us that he SPENDS 3/5 of his salary (M).
So his monthly EXPENDITURES = 3M/5
------------------------
If his monthly salary increased by 7/13, then the NEW salary = M + (7/13 of M)
= M + (7M/13)
= 13M/13 + 7M/13
= 20M/13
Since his expenditures remain at 3M/5, the NEW amount saved = 20M/13 - 3M/5
= 100M/65 - 39M/65
= 61M/65
------------------------
Ratio of NEW savings to OLD savings = (61M/65)/(2M/5)
= (61M/65)(5/2M)
= 305M/130M
= 61/26
Answer: 61/26
hi Brent, thank you for
the options i have are :
a) 26:61
b) 23:41
c) 26:41
d) 27:34
e) 61:26
Ahhh. I was wondering what
Ahhh. I was wondering what "expenditure remains unchanged" meant.
I read it as still spending 3/5 of his salary (i.e., still saving 2/5 of his salary), whereas the answer choices tell me that he saves the same AMOUNT of money as he did previously (as opposed to the same FRACTION)
I have revised my above response accordingly.
thank you!
Here i made a slight mistake.
S-1: I have considered c=3a. and written as a:b:c = c/3:c/2:3a.. so insufficient.
S-2: I missed out 6*1=6 concept and chose B as sufficient.
Cant we consider c=3a in statement 1?
For statement 1, you did
For statement 1, you did everything correctly to get c/3 : c/2 : 3a
From here, since we know c = 3a, we can take the last term above and replace 3a with c
When we do this we get c/3 : c/2 : c
To create an equivalent ratio, multiply all terms by 6 to get 2c : 3c : 6c
Divide all terms by c to get 2 : 3 : 6
For statement 1 is it
Partially. We also need the
Partially. We also need the fact that the other two variables (a and b) also appear in both fractions.
Can I understand statement 1
Can I understand statement 1 as c:a = 1:3 and c:b= 1:2,
so a to c and c to b is 3:1:2
That's not quite right.
That's not quite right.
The necessary property here says that k = k/1.
For example 3 = 3/1.
They've statement 1 says that c/a = 3.
This is the same as saying c/a = 3/1
Similarly, c:a = 3:1 (not 1:3)
The same applies to c/b = 2.
We can rewrite this as c/b = 2:1
In other words c:b = 2:1
Does that help?