GMAT Question of the Day: Daily via email | Daily via Instagram New to GMAT Club? Watch this Video

 It is currently 02 Jul 2020, 05:29 ### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

#### Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.  # Alex deposited x dollars into a new account that earned 8

Author Message
TAGS:

### Hide Tags

Intern  Joined: 27 May 2011
Posts: 5
Alex deposited x dollars into a new account that earned 8  [#permalink]

### Show Tags

18
122 00:00

Difficulty:   35% (medium)

Question Stats: 76% (02:21) correct 24% (02:41) wrong based on 2650 sessions

### HideShow timer Statistics

Alex deposited x dollars into a new account that earned 8 percent annual interest, compounded annually. One year later Alex deposited an additional x dollars into the account. If there were no other transactions and if the account contained w dollars at the end of two years, which of the following expresses x in terms of w ?

A. w/(1+1.08)
B. w/(1.08+1.16)
C. w/(1.16+1.24)
D. w/(1.08+1.08^2)
E. w/(1.08^2+1.08^2)

Originally posted by kajolnb on 23 Jan 2012, 12:12.
Last edited by MikeScarn on 03 Jul 2019, 03:58, edited 2 times in total.
Magoosh GMAT Instructor G
Joined: 28 Dec 2011
Posts: 4483
Re: Alex deposited x dollars into a new account that earned 8  [#permalink]

### Show Tags

43
16
Hi there! I'm happy to contribute to this one! The question: Alex deposited x dollars into a new account that earned 8 percent annual interest, compounded annually. One year later Alex deposited an additional x dollars into the account. If there were no other transactions and if the account contained w dollars at the end of two years, which of the following expresses x in terms of w?

So first, Alex puts in x dollars.

One year goes by, and the x dollar accrues interest ---> x(1.08)

Then, Alex adds another x dollars --> x + x(1.08)

Then the second year goes by, and that whole amount gets multiplied by 1.08 ---> [x + x(1.08)]*(1.08) = x(1.08) + x(1.08)^2 = x[1.08 + (1.08)^2]

We are told this amount, the sum total after two years, equals w, so w = x[1.08 + (1.08)^2]

Dividing by the brackets to solve for x, we get x = w/(1.08 + (1.08)^2)

The answer choices as they appear in your post are technically incorrect, because they are lacking parentheses. If you underestimate the importance of parentheses, they will bite you in the butt over and over again on the real GMAT. Assuming the parentheses were in the right places, the answer would be .

The key idea is: the x dollar amount that was in there for both years is multiplied twice by the multiplier. That's why there has to be a factor of (1.08)^2 floating around somewhere.

Does this make sense? Please let me know if you have any questions on what I've said.

Mike _________________
Mike McGarry
Magoosh Test Prep

Education is not the filling of a pail, but the lighting of a fire. — William Butler Yeats (1865 – 1939)
##### General Discussion
Math Expert V
Joined: 02 Sep 2009
Posts: 64891
Re: Alex deposited x dollars into a new account that earned 8  [#permalink]

### Show Tags

6
14
kajolnb wrote:
Alex deposited x dollars into a new account that earned 8 percent annual interest, compounded annually. One year later Alex deposited an additional x dollars into the account. If there were no other transactions and if the account contained w dollars at the end of two years, which of the following expresses x in terms of w ?

A. w/(1+1.08)
B. w/(1.08+1.16)
C. w/(1.16+1.24)
D. w/(1.08+1.08^2)
E. w/(1.08^2+1.08^2)

I thought as
1.08x+2x(1.08) = w

Account at the end of the first year would be 1.08x dollars. At this time x dollars was deposited, hence the account at the beginning of the second year would be (1.08x+x) dollars. Account at the end of the second year would be (1.08x+x)*1.08=w --> x(1.08^2+1.08)=w --> x=w/(1.08+1.08^2).

_________________
Magoosh GMAT Instructor G
Joined: 28 Dec 2011
Posts: 4483
Re: Alex deposited x dollars into a new account that earned 8  [#permalink]

### Show Tags

6
1
idinuv wrote:
I did quick math (1.08)^2 = 1.16 and selected option B.

I know option D is more precise, but can GMAC give two option different only by third decimal digit (1.16 Vs 1.1664)?

Dear idinuv,
I'm happy to respond. The short answer to your question is: "absolutely." Math is all about precision. Yes, in many Quant questions, GMAC spreads out the answer choices and allows for estimation and quick approximations, but that is not always the case. One way to think about it is that, for a pure mathematician, there is a continuous infinity of decimals between 1.16 and 1.1664 --- more decimals in that separation than the number of grains of sand it would take to fill the Universe. For a pure mathematician, there is just equal or completely unequal, and any inequality, no matter how small, is vast beyond all reckoning. Another perspective is what business people care about. Suppose, for the sake of argument, that x = \$100,000,000 --- then, whether we divide by 1.16 or 1.1664 results in a difference of \$437,014.52 : do you want that discrepancy to come out of your paycheck, because you were the person who rounded to two decimal places? Small decimal difference get very big in a hurry when one starts dealing with numbers in the millions & billions --- which values, of course, are typical in some industries. ------ Both the perspective of the pure mathematician and the perspective of big business are very important in informing the design of GMAT Quant questions, and from the point of view of both of these perspectives, the difference between 1.16 and 1.1664 could be tremendously important, not something to overlook.
Does all this make sense?
Mike _________________
Mike McGarry
Magoosh Test Prep

Education is not the filling of a pail, but the lighting of a fire. — William Butler Yeats (1865 – 1939)
Math Expert V
Joined: 02 Sep 2009
Posts: 64891
Re: Alex deposited x dollars into a new account that earned 8  [#permalink]

### Show Tags

5
2
Skag55 wrote:
Bunuel wrote:
kajolnb wrote:
Alex deposited x dollars into a new account that earned 8 percent annual interest, compounded annually. One year later Alex deposited an additional x dollars into the account. If there were no other transactions and if the account contained w dollars at the end of two years, which of the following expresses x in terms of w ?

A. w/(1+1.08)
B. w/(1.08+1.16)
C. w/(1.16+1.24)
D. w/(1.08+1.08^2)
E. w/(1.08^2+1.08^2)

I thought as
1.08x+2x(1.08) = w

Account at the end of the first year would be 1.08x dollars. At this time x dollars was deposited, hence the account at the beginning of the second year would be (1.08x+x) dollars. Account at the end of the second year would be (1.08x+x)*1.08=w --> x(1.08^2+1.08)=w --> x=w/(1.08+1.08^2).

I did the math, 1.08x + x = 2.08x
2.08x * 1.08 = 2.2464
couldn't spot the answer after 2+ mins.

How are we supposed to know to leave (1.08x + x) in order to see the cube to 1.08^2 x?

On the PS section always look at the answer choices before you start to solve a problem. They might often give you a clue on how to approach the question.

For this question this would give you a hint that you shouldn't calculate 1.08^2+1.08.
_________________
Intern  Joined: 22 Jun 2016
Posts: 47
Re: Alex deposited x dollars into a new account that earned 8  [#permalink]

### Show Tags

4
BrainLab wrote:
See attachment for the solution

might be a dumb question but at the end of 2nd year, why is it being multiplied by 1.08? should not it be multiplied by 0.08 since it is 8 %? then the resulting amount can be added back to the amount at the end of first year
Magoosh GMAT Instructor G
Joined: 28 Dec 2011
Posts: 4483
Re: Alex deposited x dollars into a new account that earned 8  [#permalink]

### Show Tags

4
cuhmoon wrote:
This maybe a foolish question but how does one know the amount was compounded for the second year also or that compounding needs to be done again on the amount?

Why isn't the solution just using the amount and adding x to the amount: (1.08x+x)

Dear cuhmoon,

I'm happy to respond. You may find this blog article helpful:
Compound Interest on the GMAT

My friend, please don't be afraid of asking a question because it might appear "foolish." Every basic question you ask that gets answered by an expert will there to help dozens of other GC users who were afraid to ask that same question.

The big idea of compound interest is interest on interest. If we compounded in the first year, and then stopped, that wouldn't be compound interest. The action of compounding is when new interest starts to accrue on interest already there.

If x is the initial amount, notice that 0.08x is 8% of x--that would be just the interest after one cycle, if the interest rate were 8%. If we want interest plus principal, we add x + 0.08x = 1x + 0.08x = 1.08x. That latter form, 1.08x is a 8% increase on a starting value of x; it's the value of interest plus principal after one cycle. Notice that the question very specifically says: "One year later Alex deposited an additional x dollars into the account." In other words, this is not just a single one-time deposit of principal that is building up interest: instead, Alex put money in, let it build up interest, and then put more money in from the outside. After the first year, 1.08x was already in the account, after the interest was added, and then separate from the process of interest, Alex deposited another x of his own money into this same account. That's why we add 1.08x + x.

In order to understand all this, it's very helpful to understand percents and percent changes as multipliers.

Does all this make sense?
Mike _________________
Mike McGarry
Magoosh Test Prep

Education is not the filling of a pail, but the lighting of a fire. — William Butler Yeats (1865 – 1939)
Manager  S
Joined: 24 Oct 2016
Posts: 238
Location: India
Schools: IIMB
GMAT 1: 550 Q42 V28
GPA: 3.96
WE: Human Resources (Retail Banking)
Re: Alex deposited x dollars into a new account that earned 8  [#permalink]

### Show Tags

2
suppose X = 800
and given R= 8 compounded annually
now 800(1.08) ....... for first year
so 800(1.08)^2.......for 2nd year and now as he added 800 after 1 year then calculate that separately as earlier 800(1.08)

W= 800(1.08)^2+ 800(1.08)

as we need to calculate X in terms of W ,
so look for the option now Check E first which will not give us 800

now look for option D , in which by solving we get ....
800{(1.08)^2+(1.08)}/ (1.08)^2+ (1.08)
= 800=X
hence D

hit kudos to appreciate . Manager  Joined: 26 Feb 2013
Posts: 145
Re: Alex deposited x dollars into a new account that earned 8  [#permalink]

### Show Tags

1
Bunuel wrote:
kajolnb wrote:
Alex deposited x dollars into a new account that earned 8 percent annual interest, compounded annually. One year later Alex deposited an additional x dollars into the account. If there were no other transactions and if the account contained w dollars at the end of two years, which of the following expresses x in terms of w ?

A. w/(1+1.08)
B. w/(1.08+1.16)
C. w/(1.16+1.24)
D. w/(1.08+1.08^2)
E. w/(1.08^2+1.08^2)

I thought as
1.08x+2x(1.08) = w

Account at the end of the first year would be 1.08x dollars. At this time x dollars was deposited, hence the account at the beginning of the second year would be (1.08x+x) dollars. Account at the end of the second year would be (1.08x+x)*1.08=w --> x(1.08^2+1.08)=w --> x=w/(1.08+1.08^2).

I did the math, 1.08x + x = 2.08x
2.08x * 1.08 = 2.2464
couldn't spot the answer after 2+ mins.

How are we supposed to know to leave (1.08x + x) in order to see the cube to 1.08^2 x?
Intern  Joined: 21 Mar 2013
Posts: 37
GMAT Date: 03-20-2014
Re: Alex deposited x dollars into a new account that earned 8  [#permalink]

### Show Tags

1
Bunuel wrote:
kajolnb wrote:
Alex deposited x dollars into a new account that earned 8 percent annual interest, compounded annually. One year later Alex deposited an additional x dollars into the account. If there were no other transactions and if the account contained w dollars at the end of two years, which of the following expresses x in terms of w ?

A. w/(1+1.08)
B. w/(1.08+1.16)
C. w/(1.16+1.24)
D. w/(1.08+1.08^2)
E. w/(1.08^2+1.08^2)

I thought as
1.08x+2x(1.08) = w

Account at the end of the first year would be 1.08x dollars. At this time x dollars was deposited, hence the account at the beginning of the second year would be (1.08x+x) dollars. Account at the end of the second year would be (1.08x+x)*1.08=w --> x(1.08^2+1.08)=w --> x=w/(1.08+1.08^2).

I did quick math (1.08)^2 = 1.16 and selected option B.

I know option D is more precise, but can GMAC give two option different only by third decimal digit (1.16 Vs 1.1664)?
Intern  Joined: 21 Mar 2013
Posts: 37
GMAT Date: 03-20-2014
Re: Alex deposited x dollars into a new account that earned 8  [#permalink]

### Show Tags

1
mikemcgarry wrote:
idinuv wrote:
I did quick math (1.08)^2 = 1.16 and selected option B.

I know option D is more precise, but can GMAC give two option different only by third decimal digit (1.16 Vs 1.1664)?

Dear idinuv,
I'm happy to respond. The short answer to your question is: "absolutely." Math is all about precision. Yes, in many Quant questions, GMAC spreads out the answer choices and allows for estimation and quick approximations, but that is not always the case. One way to think about it is that, for a pure mathematician, there is a continuous infinity of decimals between 1.16 and 1.1664 --- more decimals in that separation than the number of grains of sand it would take to fill the Universe. For a pure mathematician, there is just equal or completely unequal, and any inequality, no matter how small, is vast beyond all reckoning. Another perspective is what business people care about. Suppose, for the sake of argument, that x = \$100,000,000 --- then, whether we divide by 1.16 or 1.1664 results in a difference of \$437,014.52 : do you want that discrepancy to come out of your paycheck, because you were the person who rounded to two decimal places? Small decimal difference get very big in a hurry when one starts dealing with numbers in the millions & billions --- which values, of course, are typical in some industries. ------ Both the perspective of the pure mathematician and the perspective of big business are very important in informing the design of GMAT Quant questions, and from the point of view of both of these perspectives, the difference between 1.16 and 1.1664 could be tremendously important, not something to overlook.
Does all this make sense?
Mike Thanks for your clear explanation Mike !

I totally concede with both the perspectives you have put-forth. My perspective about the design of incorrect answers has been that the incorrect answers generally are Partial answers, Wrong path answers, Simple manipulation answers etc. As suggested, I would now also lookout for 'Precision' based on the range of answer choices given.
Current Student B
Joined: 10 Mar 2013
Posts: 448
Location: Germany
Concentration: Finance, Entrepreneurship
Schools: WHU MBA"20 (A\$)
GMAT 1: 580 Q46 V24
GPA: 3.88
WE: Information Technology (Consulting)
Re: Alex deposited x dollars into a new account that earned 8  [#permalink]

### Show Tags

1
1
See attachment for the solution
Attachments PS 99.JPG [ 19.33 KiB | Viewed 44740 times ]

Intern  B
Joined: 23 Sep 2016
Posts: 10
Location: India
Concentration: Operations, Strategy
GMAT 1: 750 Q50 V41
GPA: 3
WE: Operations (Energy and Utilities)
Re: Alex deposited x dollars into a new account that earned 8  [#permalink]

### Show Tags

1
1.08(1.08x + x) = (1.08^2)x + 1.08x

The new total value obtained is equal to w, we can set up the following equation:

w = (1.08^2)x + 1.08x

So, X in terms of w

w = x(1.08^2 + 1.08)

w/(1.08^2 + 1.08) = x

Intern  B
Joined: 03 Apr 2018
Posts: 37
Re: Alex deposited x dollars into a new account that earned 8  [#permalink]

### Show Tags

1
yonseiglobalstudent wrote:
BrainLab wrote:
See attachment for the solution

I just want to clarify one point. I follow up until the start of the 2nd year, but then why do we multiply again by 1.08? (2.08x)(1.08)
Where did the 1.08 come from? I believe we need to represent 8% of 2.08x, but why don't we multiply by .08 instead?

I have the same question. Can someone please explain clearly why we are multiplying by 1.08 and not 0.08 at the end of the second year?
Math Expert V
Joined: 02 Sep 2009
Posts: 64891
Re: Alex deposited x dollars into a new account that earned 8  [#permalink]

### Show Tags

1
shreyagupta1401 wrote:
yonseiglobalstudent wrote:
BrainLab wrote:
See attachment for the solution

I just want to clarify one point. I follow up until the start of the 2nd year, but then why do we multiply again by 1.08? (2.08x)(1.08)
Where did the 1.08 come from? I believe we need to represent 8% of 2.08x, but why don't we multiply by .08 instead?

I have the same question. Can someone please explain clearly why we are multiplying by 1.08 and not 0.08 at the end of the second year?

Interest earned at the end of the second year would be 2.08x*0.08 but the balance at the end of the second year would be (amount at the beginning of the second year) + (interest earned in second year) = 2.08x + 2.08x*0.08 = 2.08x*1.08.

Hope it's clear.
_________________
Manager  Joined: 26 Feb 2013
Posts: 145
Re: Alex deposited x dollars into a new account that earned 8  [#permalink]

### Show Tags

Got it, wasn't aware of this. Thanks!
Target Test Prep Representative V
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 10998
Location: United States (CA)
Re: Alex deposited x dollars into a new account that earned 8  [#permalink]

### Show Tags

kajolnb wrote:
Alex deposited x dollars into a new account that earned 8 percent annual interest, compounded annually. One year later Alex deposited an additional x dollars into the account. If there were no other transactions and if the account contained w dollars at the end of two years, which of the following expresses x in terms of w ?

A. w/(1+1.08)
B. w/(1.08+1.16)
C. w/(1.16+1.24)
D. w/(1.08+1.08^2)
E. w/(1.08^2+1.08^2)

We start by determining the new value of the x dollars Alex deposited into his account that earned 8 percent annual interest. At the end of the first year the amount of money in the account was 1.08x and then he added another x dollars to the account, so the account then had a total value of 1.08x + x dollars. The 1.08x + x dollars earned another 8 percent interest for the year. Thus, the total value of his account at the end of the second year is:

1.08(1.08x + x) = (1.08^2)x + 1.08x

Since the new total value is equal to w, we can set up the following equation:

w = (1.08^2)x + 1.08x

Now we must get x in terms of w.

w = x(1.08^2 + 1.08)

w/(1.08^2 + 1.08) = x

_________________

# Scott Woodbury-Stewart

Founder and CEO

Scott@TargetTestPrep.com

See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews

Manager  B
Joined: 30 Jun 2015
Posts: 50
Location: Malaysia
Schools: Babson '20
GPA: 3.6
Re: Alex deposited x dollars into a new account that earned 8  [#permalink]

### Show Tags

This maybe a foolish question but how does one know the amount was compounded for the second year also or that compounding needs to be done again on the amount?

Why isn't the solution just using the amount and adding x to the amount: (1.08x+x)

Bunuel wrote:
kajolnb wrote:
Alex deposited x dollars into a new account that earned 8 percent annual interest, compounded annually. One year later Alex deposited an additional x dollars into the account. If there were no other transactions and if the account contained w dollars at the end of two years, which of the following expresses x in terms of w ?

A. w/(1+1.08)
B. w/(1.08+1.16)
C. w/(1.16+1.24)
D. w/(1.08+1.08^2)
E. w/(1.08^2+1.08^2)

I thought as
1.08x+2x(1.08) = w

Account at the end of the first year would be 1.08x dollars. At this time x dollars was deposited, hence the account at the beginning of the second year would be (1.08x+x) dollars. Account at the end of the second year would be (1.08x+x)*1.08=w --> x(1.08^2+1.08)=w --> x=w/(1.08+1.08^2).

Intern  B
Joined: 15 Dec 2017
Posts: 12
Re: Alex deposited x dollars into a new account that earned 8  [#permalink]

### Show Tags

BrainLab wrote:
See attachment for the solution

I just want to clarify one point. I follow up until the start of the 2nd year, but then why do we multiply again by 1.08? (2.08x)(1.08)
Where did the 1.08 come from? I believe we need to represent 8% of 2.08x, but why don't we multiply by .08 instead?
Manager  B
Joined: 30 Jul 2014
Posts: 103
GPA: 3.72
Re: Alex deposited x dollars into a new account that earned 8  [#permalink]

### Show Tags

I forgot adding the interest earned in the second year, and thus the result was option A - I did this silly mistake..
_________________
A lot needs to be learned from all of you. Re: Alex deposited x dollars into a new account that earned 8   [#permalink] 11 May 2018, 08:27

Go to page    1   2    Next  [ 22 posts ]

# Alex deposited x dollars into a new account that earned 8   