Two hard questions ?

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vanesslondon: Senior | Next Rank: 100 Posts; Posts: 62; Joined: Mon May 21, 2007 12:00 am

by vanesslondon » Fri Oct 17, 2008 3:39 am

Dear fellow posters,

My test is next week and I did a GMAT prep exam and couldn't answer the below questions (which I think might test the same concept). Could someone please help me out? Also if you know what kind of questions these are please let me know so I can revise them.

Many many thanks!

Question 1

An investment of d $ at k percent annual interest yield $600 interest over a 2 year period. In terms of d what $ amount invested at the same rate yields $2400?

A. 2d/3

B. 3d/4

C. 4d/3

D. 3d/2

E. 8d/3

(Answer D)

Question 2

There are 3 grades of milk, 1%, 2% and 3% fat by volume. x gallons of 1% milk, y gallons of 2% milk and z gallons of 3% milk are mixed to give x+y+Z gallons of 1.5% milk. What is x in terms of y+z?

A: y+3z

B. y+3/4

C. 2y + 3z

D. 3y + z

E. 3y+4.5z

(Answer C)

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Source: Beat The GMAT — Problem Solving | Fri Oct 17, 2008 3:39 am

ankit1383: Master | Next Rank: 500 Posts; Posts: 159; Joined: Sun Jul 27, 2008 8:41 pm; Thanked: 3 times

Hi

by ankit1383 » Fri Oct 17, 2008 4:19 am

For second Question...answer should be y+3z..............can anyone explainthe correct answer for second question

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dally_gmat: Senior | Next Rank: 100 Posts; Posts: 31; Joined: Mon Sep 15, 2008 6:16 pm; Thanked: 3 times

Re: Two hard questions ?

by dally_gmat » Fri Oct 17, 2008 8:13 am

What is the time for which money is invested when the yield is $2400?

vanesslondon wrote:Dear fellow posters,

Question 1

An investment of d $ at k percent annual interest yield $600 interest over a 2 year period. In terms of d what $ amount invested at the same rate yields $2400?

A. 2d/3

B. 3d/4

C. 4d/3

D. 3d/2

E. 8d/3

(Answer D)

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dally_gmat: Senior | Next Rank: 100 Posts; Posts: 31; Joined: Mon Sep 15, 2008 6:16 pm; Thanked: 3 times

Re: Two hard questions ?

by dally_gmat » Fri Oct 17, 2008 8:18 am

Here is my take:

(x*1/100 + y*2/100 + z*3/100) = 1.5*1/100 (x+y+z))
Solving

.5y+1.5z = .5x
or y+3z = x

But it does not matches answer..

Any other replies?

vanesslondon wrote:Dear fellow posters,

Question 2

There are 3 grades of milk, 1%, 2% and 3% fat by volume. x gallons of 1% milk, y gallons of 2% milk and z gallons of 3% milk are mixed to give x+y+Z gallons of 1.5% milk. What is x in terms of y+z?

A: y+3z

B. y+3/4

C. 2y + 3z

D. 3y + z

E. 3y+4.5z

(Answer C)

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willbeatthegmat: Senior | Next Rank: 100 Posts; Posts: 71; Joined: Sat Sep 20, 2008 5:48 am; Thanked: 5 times

by willbeatthegmat » Sat Oct 18, 2008 12:45 am

Q- An investment of d $ at k percent annual interest yield $600 interest over a 2 year period. In terms of d what $ amount invested at the same rate yields $2400?

A. 2d/3

B. 3d/4

C. 4d/3

D. 3d/2

E. 8d/3

Ans: Assume a number for d. let d=1000
since we know tat d(1000) at k%p.a. yield $600 interest in 2 yrs, we can take k=30%
Verify: 2(1000*30/100)= 600(which is simply 60% of 1000

Now we have to find out the amount invested at the same rate(30%) for the same period wud yield 2400(principal amount + interest)

Let amount invested be x
x+x*60/100 = 2400
x = 1500

Our target answer is 1500. Try pluggin in wid d=1000 n only option D yields the same answer.

Hope it works
Can any1 else suggest me the better way to approach dis question

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vanesslondon: Senior | Next Rank: 100 Posts; Posts: 62; Joined: Mon May 21, 2007 12:00 am

by vanesslondon » Sat Oct 18, 2008 6:13 am

Thanks so much - you guys are just brilliant!

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gmat009: Master | Next Rank: 500 Posts; Posts: 458; Joined: Sun Aug 31, 2008 10:44 amFollowed by: 1 member; Thanked: 3 times

by gmat009 » Mon Oct 20, 2008 12:20 pm

I am not sure where I am making mistake but I am getting 4d answer.
Can someone plz help me.
Here is how I apporached-
600=d(1+k/100)^2
k/100= (600/d)^1/2 -1

2400=P(1+k/100)^2
2400=P(1+((600/d)^1/2 -1))^2
Therefore P=4d

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ltg356: Newbie | Next Rank: 10 Posts; Posts: 6; Joined: Tue Oct 21, 2008 7:16 am

by ltg356 » Tue Oct 21, 2008 7:24 am

gmatt009,

I was hung up on this too. In business terms, yield is the return on investment, not principal plus interest.

This question assumes yield to be principal plus interest, I guess you have to look at the answer choices to see that. Seems like an unfair waste of time, but oh well.

Also assumed by the answer choices is simple interest, although not explicitly stated in the question. Is there any method to when simple or compound interest is assumed other than by looking at the answer choices?

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dilbert: Newbie | Next Rank: 10 Posts; Posts: 3; Joined: Wed Oct 22, 2008 6:09 am

for question #1

by dilbert » Thu Oct 23, 2008 2:01 pm

it was answered before:

https://www.beatthegmat.com/gmat-prep-in ... t9813.html

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rohangupta83: Legendary Member; Posts: 541; Joined: Thu May 31, 2007 6:44 pmFollowed by: 3 members; Location: UK; Thanked: 21 times; GMAT Score:680

by rohangupta83 » Fri Oct 24, 2008 2:00 am

gmat009 wrote:I am not sure where I am making mistake but I am getting 4d answer.
Can someone plz help me.
Here is how I apporached-
600=d(1+k/100)^2
k/100= (600/d)^1/2 -1

2400=P(1+k/100)^2
2400=P(1+((600/d)^1/2 -1))^2
Therefore P=4d

you are correct. I am also getting the same answer. It has to be 4d unless the time period is different. And if the time period is different we won't be able to solve using the compound interest formula.

Last edited by rohangupta83 on Fri Oct 24, 2008 2:10 am, edited 1 time in total.

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rohangupta83: Legendary Member; Posts: 541; Joined: Thu May 31, 2007 6:44 pmFollowed by: 3 members; Location: UK; Thanked: 21 times; GMAT Score:680

by rohangupta83 » Fri Oct 24, 2008 2:09 am

This is the correct question:

An investment of d dollars at k percent simple annual interest yields $600 interest over a 2 yr period. In terms of d, what dollar amount invested at the same rate will yield $2,400 interest over a 3 yr period?

a. 2d/3
b. 3d/4
c. 4d/3
d. 3d/2
e. 8d/3

OA - E

vanesslondon - please check whether the question i posted here is correct or not.

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rohangupta83: Legendary Member; Posts: 541; Joined: Thu May 31, 2007 6:44 pmFollowed by: 3 members; Location: UK; Thanked: 21 times; GMAT Score:680

by rohangupta83 » Fri Oct 24, 2008 2:18 am

answer to the second question is (A)

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sudhir3127: Legendary Member; Posts: 829; Joined: Mon Jul 07, 2008 10:09 pmFollowed by: 3 members; Location: INDIA; Thanked: 84 times

by sudhir3127 » Fri Oct 24, 2008 3:56 am

rohangupta83 wrote:This is the correct question:

An investment of d dollars at k percent simple annual interest yields $600 interest over a 2 yr period. In terms of d, what dollar amount invested at the same rate will yield $2,400 interest over a 3 yr period?

a. 2d/3
b. 3d/4
c. 4d/3
d. 3d/2
e. 8d/3

OA - E

vanesslondon - please check whether the question i posted here is correct or not.

Simple interest = PRT/100
600 = d*k*2/100
60000/2 = dk
30000= dk.................................................1

2400 = x*k*3/100
240000/3 = xK
80000= xk.............................................2

from 1 and 2 we know that
X = 8d/3....

hence E.

Hope thats clear.. do let me know if u have any doubts..

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cramya: Legendary Member; Posts: 2467; Joined: Thu Aug 28, 2008 6:14 pmFollowed by: 11 members; Thanked: 331 times

Re: Two hard questions ?

by cramya » Fri Oct 24, 2008 6:29 am

dally_gmat wrote:Here is my take:

(x*1/100 + y*2/100 + z*3/100) = 1.5*1/100 (x+y+z))
Solving

.5y+1.5z = .5x
or y+3z = x

But it does not matches answer..

Any other replies?

vanesslondon wrote:Dear fellow posters,

Question 2

There are 3 grades of milk, 1%, 2% and 3% fat by volume. x gallons of 1% milk, y gallons of 2% milk and z gallons of 3% milk are mixed to give x+y+Z gallons of 1.5% milk. What is x in terms of y+z?

A: y+3z

B. y+3/4

C. 2y + 3z

D. 3y + z

E. 3y+4.5z

(Answer C)

Dally,
The correct answer to this problem is A) and not C)
You got it right. Good luck!

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