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DS problems - answers right?

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DS problems - answers right?

by Kelly » Thu Sep 10, 2009 9:34 am
Hi, I reviewed these problems again & agian, but I cannot figure out why I got wrong.

The operation* represents either addition, subtraction, or multiplication of integers, what is the value of 1*0?

(1) 0*2=2
(2) 2*0=2

the answer is A, but I think it isD.

From May 1 to May 30 in the same year, the balance in a checking account increased. What was the balance in the checking account on May 30?

(1) If, during this period of time, the increase in the balance in the checking account had been 12 percent, then the balance in the account on May 30 would have been $504
(2) During this period of time, the increase in the balance in the checking account was 8 percent.

the answer is A, but I think it isC.
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by bharathh » Thu Sep 10, 2009 10:37 am
Q1

Statement 1

Take all 4 operations 1 at a time.

0+2 = 2? Yes
0-2 = 2? No
0/2 = 2? No
0*2 = 2? No

1 is sufficient.

Statement 2

2+0 = 2?Yes
2-0 = 2?Yes

You can stop here... If you just considered statement 2 you cannot state that the operation is + or - However with Statement 1 you can. Answer is A



Q2

From question

You have an end balance = E
You have a starting balance = S

% Increase in balance = 100*(E-S)/S

Statement 1

You are told % increase in balance and end balance. If you substitute into the equation above, there is only 1 variable to find. 1 variable equations can be solved. Sufficient.

e.g. 12 = 100*(504-S)/S
NOTE: You don't have to solve for S.. just know it's possible


Statement 2

You are only give one piece of information.

8 = 100*(E-S)/S

There are still 2 unknown variables. So this is not enough to get a value for S. So insufficient.

Answer is A
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by gmatpill » Thu Sep 10, 2009 12:47 pm
The operation* represents either addition, subtraction, or multiplication of integers, what is the value of 1*0?

(1) 0*2=2
(2) 2*0=2
I'm actually going to stick my neck out and disagree with the answer on this one. I believe you mentioned the answer here is (A). I am going to say (D) and here's why.

Let's follow through some of the analysis so far:

Statement 1

0+2 = 2? Yes
0-2 = 2? No
0/2 = 2? No
0*2 = 2? No

(1) is sufficient.

Statement 2

2+0 = 2?Yes
2-0 = 2?Yes

With (1) you DEFINITELY know * must be +. So Statement (1) is good.

With (2), it could be EITHER "+" or "-". There is indeed ambiguity regarding which operation you should use.

But look carefully at the question. It asks:
what is the value of 1*0?

Well, let's break it down with the two operations: addition and subtraction.

what is the value of 1+0?
What is the value of 1-0?

Notice the answer to each of the two situations is 1! There is NO ambiguity to the question. The answer is always 1 regardless of addition or subtraction.

Remember you need to answer the question and not get confused with the intermediary steps. When there is no ambiguity to the question then you know you do indeed have enough information. Therefore, (2) alone is good as well as (1) alone. So the overall answer is (D).

If I missed a point, please point out, but this seems like a typical way GMAT tries to trick you.

Your second question...
From May 1 to May 30 in the same year, the balance in a checking account increased. What was the balance in the checking account on May 30?

(1) If, during this period of time, the increase in the balance in the checking account had been 12 percent, then the balance in the account on May 30 would have been $504
(2) During this period of time, the increase in the balance in the checking account was 8 percent.
Now with your second question, I do agree the answer is (A). Let's take a look.

There are three areas:
1) Beginning
2) Percentage change
3) End

The question asks what was the end balance---basically it's like for item #3. This is a typical framework of the GMAT Pill. You basically need two of the 3 in order to find the last piece. So in order to find the end balance, you need both the beginning balance and the percentage change in between.

With statement (1) you see a percentage change and you also see a number. And actually it's even easier than I expected: they flat out tell you what the balance is on May 30. So statement (1) is good.

With statement (2) I see a percentage but i don't see an actual number. Since I do not see an actual number, there is no way statement (2) could possibly be good.

So when statement (1) is good and (2) is no good, the overall answer is (A).
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by bharathh » Thu Sep 10, 2009 12:57 pm
Hmm... you make a good poitn about Q1. Why do you think the OA is A then? Perhaps a mistake in the question itself?
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by Ian Stewart » Thu Sep 10, 2009 3:40 pm
gmatpill wrote: Now with your second question, I do agree the answer is (A). Let's take a look.

There are three areas:
1) Beginning
2) Percentage change
3) End

The question asks what was the end balance---basically it's like for item #3. This is a typical framework of the GMAT Pill. You basically need two of the 3 in order to find the last piece. So in order to find the end balance, you need both the beginning balance and the percentage change in between.

With statement (1) you see a percentage change and you also see a number. And actually it's even easier than I expected: they flat out tell you what the balance is on May 30. So statement (1) is good.
You're right about the first question, but not about the second. Statement 1 only tells you the final balance if the increase was 12%. We have no idea what the actual increase was, so the first Statement is nowhere close to being sufficient - the increase may have been 1%, or it may have been 5000%. If that's the 'framework of the GMAT pill', whatever that is supposed to mean, the pill needs a new formulation.

Kelly - your answers are correct to both questions. Where are the OAs from? They are clearly wrong, and you're right.
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by estode » Thu Sep 10, 2009 3:47 pm
I thought the answer to question 2 was C as well. Sure, you can find the starting balance on May 1st by using 12% and $504. However, at the beginning of Statement 1, it reads:

"If, during this period of time, the increase in the balance in the checking account had been 12 percent...."

The use of the word "if" makes me think that this a hypothetical percentage, and not definitive. Can anyone clarify this answer further? Or am I thinking too much/missing something?

Statement 2 gives a definitive percentage - 8%.

Thanks!

Edit: Thanks Ian... you answered my question perfectly.
Last edited by estode on Thu Sep 10, 2009 4:41 pm, edited 2 times in total.
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by gmatpill » Thu Sep 10, 2009 4:22 pm
"If, during this period of time, the increase in the balance in the checking account had been 12 percent...."

Based on the bolded words in this phrase in statement (1), I would say it does not definitively tell you what the ending balance was. I knew something was fishy when it appeared they blatantly gave you the ending balance--too good to be true!

However, this statement basically indirectly tells you the BEGINNING balance.

In order to definitely find the ENDING balance, you need TWO pieces of information:
1) The beginning balance (which the above statement basically tells you)
2) The % increase (which statement 2 tells you.

Therefore, based on this re-read of the hypothetical bolded words in statement (1), the answer would be (C).
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by bharathh » Fri Sep 11, 2009 3:46 am
Ian Stewart wrote:You're right about the first question, but not about the second. Statement 1 only tells you the final balance if the increase was 12%. We have no idea what the actual increase was, so the first Statement is nowhere close to being sufficient - the increase may have been 1%, or it may have been 5000%. If that's the 'framework of the GMAT pill', whatever that is supposed to mean, the pill needs a new formulation.
I disagree with this point. Yesterday when you typed this up I figured you were correct. However during my GMATPrep test last night, I ran into a few PS question stems that provided me information using those words.

If x had been ... what is the value of y

If what you say is true then there should be an option that says cannot calculate the answer. However there was none.

Given this, I think my answer to Q2 is correct. I agree wholeheartedly that D is correct for Q1.

Here's an example of a problem I solved last night

The ratio of the amount of Alex's fuel oil bill for the month of February to the amount of his fuel oil bill for the month of January was 3/2. If the fuel oil bill for February had been $40 more, the corresponding ratio would have been 5/3. How much was Alex's fuel oil bill for January?

A. $240
B. $300
C. $360
D. $450
E. $540
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by Ian Stewart » Fri Sep 11, 2009 4:47 am
bharathh wrote: I disagree with this point. Yesterday when you typed this up I figured you were correct. However during my GMATPrep test last night, I ran into a few PS question stems that provided me information using those words.

If x had been ... what is the value of y

If what you say is true then there should be an option that says cannot calculate the answer. However there was none.

Given this, I think my answer to Q2 is correct. I agree wholeheartedly that D is correct for Q1.

Here's an example of a problem I solved last night

The ratio of the amount of Alex's fuel oil bill for the month of February to the amount of his fuel oil bill for the month of January was 3/2. If the fuel oil bill for February had been $40 more, the corresponding ratio would have been 5/3. How much was Alex's fuel oil bill for January?

A. $240
B. $300
C. $360
D. $450
E. $540
In the PS question above, you have the equivalent of *both* statements of information from the second question in Kelly's post. You know the actual ratio from January to February is 3 to 2, so you know that there was a 50% increase in the bill from January to February (that's the equivalent of Statement 2 in Kelly's question). You also know what the percent increase would have been had the February bill been different (that's roughly the equivalent of Statement 1 in Kelly's question). With both of those pieces of information, you can certainly answer the question. If F is the February bill and J the January bill, from the first ratio we know that F/J = 3/2, or that 2F = 3J. From the second piece of information, we know that the ratio of F+40 to J is 5 to 3, so (F+40)/J = 5/3, or 3F + 120 = 5J. We now have a standard set of two equations in two unknowns:

3F + 120 = 5J
2F = 3J

and multiplying the first by 3, and the second by 2, we can subtract:
6F + 240 = 10J
6F = 9J
240 = J

Compare with the other question:
Kelly wrote: From May 1 to May 30 in the same year, the balance in a checking account increased. What was the balance in the checking account on May 30?

(1) If, during this period of time, the increase in the balance in the checking account had been 12 percent, then the balance in the account on May 30 would have been $504
(2) During this period of time, the increase in the balance in the checking account was 8 percent.
We have two unknowns here: the starting balance, which I'll call S, and the closing balance, which I'll call C. From Statement 1, we know that 1.12*S = 504, so we can find the starting balance (it's 450). We are not, however, asked for the starting balance in the question; we're asked for the closing balance. Since we have no information about the increase in the balance over the month from Statement 1 alone, it is not sufficient. Statement 2 alone is not sufficient, since we have no idea what the starting or closing balances are. Combined, we know the closing balance is 8% greater than $450, so is equal to (1.08)*(450) = 486, and the two Statements together are sufficient.
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by bharathh » Fri Sep 11, 2009 5:03 am
Ah ok .. :idea:

You can find S but not C or E as I called it from statement 1.

Talk about a trap! :evil:

Ans should be C
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by heshamelaziry » Tue Sep 15, 2009 7:14 pm
gmatpill wrote:
The operation* represents either addition, subtraction, or multiplication of integers, what is the value of 1*0?

(1) 0*2=2
(2) 2*0=2
I'm actually going to stick my neck out and disagree with the answer on this one. I believe you mentioned the answer here is (A). I am going to say (D) and here's why.

Let's follow through some of the analysis so far:

Statement 1

0+2 = 2? Yes
0-2 = 2? No
0/2 = 2? No
0*2 = 2? No

(1) is sufficient.

Statement 2

2+0 = 2?Yes
2-0 = 2?Yes

With (1) you DEFINITELY know * must be +. So Statement (1) is good.

With (2), it could be EITHER "+" or "-". There is indeed ambiguity regarding which operation you should use.

But look carefully at the question. It asks:
what is the value of 1*0?

Well, let's break it down with the two operations: addition and subtraction.

what is the value of 1+0?
What is the value of 1-0?

Notice the answer to each of the two situations is 1! There is NO ambiguity to the question. The answer is always 1 regardless of addition or subtraction.

Remember you need to answer the question and not get confused with the intermediary steps. When there is no ambiguity to the question then you know you do indeed have enough information. Therefore, (2) alone is good as well as (1) alone. So the overall answer is (D).

If I missed a point, please point out, but this seems like a typical way GMAT tries to trick you.

Your second question...
From May 1 to May 30 in the same year, the balance in a checking account increased. What was the balance in the checking account on May 30?

(1) If, during this period of time, the increase in the balance in the checking account had been 12 percent, then the balance in the account on May 30 would have been $504
(2) During this period of time, the increase in the balance in the checking account was 8 percent.
Now with your second question, I do agree the answer is (A). Let's take a look.

There are three areas:
1) Beginning
2) Percentage change
3) End

The question asks what was the end balance---basically it's like for item #3. This is a typical framework of the GMAT Pill. You basically need two of the 3 in order to find the last piece. So in order to find the end balance, you need both the beginning balance and the percentage change in between.

With statement (1) you see a percentage change and you also see a number. And actually it's even easier than I expected: they flat out tell you what the balance is on May 30. So statement (1) is good.

With statement (2) I see a percentage but i don't see an actual number. Since I do not see an actual number, there is no way statement (2) could possibly be good.

So when statement (1) is good and (2) is no good, the overall answer is (A).

How about multiplication and division for statement 2, why did you check those operation in stetement 2 as you did in statwement 1 ???????
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