GMAT FOCUS QUESTION-1

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GMAT FOCUS QUESTION-1

by abhasjha » Tue Jul 15, 2014 5:56 am
An investor opened a money market account with a single deposit of $6000 on Dec. 31, 2001. The interest earned on the account was calculated and reinvested quarterly. The compound interest for the first 3 quarters of 2002 was $125, $130, and $145, respectively. If the investor made no deposits or withdrawals during the year, approximately what annual rate of interest must the account earn for the 4th quarter in order for the total interest earned on the account for the year to be 10 percent of the initial deposit?

A 3.1%
B 9.3%
C 10.0%
D 10.5%
E 12.5%
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by riskygurpreet » Tue Jul 15, 2014 6:20 am
CAN YOU TELL ME THE ANSWER???

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by GMATGuruNY » Tue Jul 15, 2014 6:24 am
abhasjha wrote:An investor opened a money market account with a single deposit of $6000 on Dec. 31, 2001. The interest earned on the account was calculated and reinvested quarterly. The compound interest for the first 3 quarters of 2002 was $125, $130, and $145, respectively. If the investor made no deposits or withdrawals during the year, approximately what annual rate of interest must the account earn for the 4th quarter in order for the total interest earned on the account for the year to be 10 percent of the initial deposit?

A 3.1%
B 9.3%
C 10.0%
D 10.5%
E 12.5%
Total amount of interest that must be earned over the entire year = 10% of 6000 = 600.
Interest earned in the first 3 quarters = 125+130+145 = 400.
Interest that must be earned in the 4th quarter = 600-400 = 200.

Amount in the account at the end of the 3rd quarter = (principal) + (interest earned in the first 3 quarters) = 6000+400 = 6400.
We can PLUG IN THE ANSWERS, which represent the annual interest rate required to earn $200 in the 4th quarter.
Since the answer choices represent the ANNUAL interest rate, 1/4 of the implied interest will be earned in the 4th quarter.

Answer choice D: 10.5%
1/4 of (10.5% of 6400) = (1/4)(10.5/100)(6400) = (10.5)(16) = 168.
To earn $200 in the 4th quarter, a higher interest rate is required.

The correct answer is E.
Last edited by GMATGuruNY on Tue Jul 15, 2014 6:42 am, edited 2 times in total.
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by Brent@GMATPrepNow » Tue Jul 15, 2014 6:25 am
abhasjha wrote:An investor opened a money market account with a single deposit of $6000 on Dec. 31, 2001. The interest earned on the account was calculated and reinvested quarterly. The compound interest for the first 3 quarters of 2002 was $125, $130, and $145, respectively. If the investor made no deposits or withdrawals during the year, approximately what annual rate of interest must the account earn for the 4th quarter in order for the total interest earned on the account for the year to be 10 percent of the initial deposit?

A 3.1%
B 9.3%
C 10.0%
D 10.5%
E 12.5%
After 3 quarters, the investment value = $6000 + $125 + $130 + $145 = $6400
We want the total interest earned on the account to be 10 percent of the initial deposit.
10% of $6000 = $600
So, we want the total interest to be $600
At the moment, the investor has received $400 in interest ($125 + $130 + $145 = $400 )
So, in the 4th quarter, the investor needs to make an additional $200 in interest.

So, what must the interest rate be to make $200 in interest from an investment currently worth $6400?
Well, $200/$6400 = 1/32 = 3.125%
So, in the 4th QUARTER, the investment must receive 3.125% interest.

The question asks us to determine the ANNUAL interest rate. So, the ANNUAL interest rate must equal (3.125%)(4) = [spoiler]12.5%[/spoiler]

Answer: E

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by abhasjha » Tue Jul 15, 2014 7:18 am

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by GMATinsight » Tue Jul 15, 2014 7:25 am
abhasjha wrote:An investor opened a money market account with a single deposit of $6000 on Dec. 31, 2001. The interest earned on the account was calculated and reinvested quarterly. The compound interest for the first 3 quarters of 2002 was $125, $130, and $145, respectively. If the investor made no deposits or withdrawals during the year, approximately what annual rate of interest must the account earn for the 4th quarter in order for the total interest earned on the account for the year to be 10 percent of the initial deposit?

A 3.1%
B 9.3%
C 10.0%
D 10.5%
E 12.5%
Amount of interest to be earned by end of 4th Quarter = 10% of $6000 = $600

Amount earned in first three quarters = 125+130+145 = $400

Remaining Amount to be earned in 4th Quarter = 600-400 = $200

But the amount after 3rd Quarter = 6000+Interest earned = 6000+400 = $6400

($6400 is the new principal as it being the case of compound Interest)
Rate of interest for earning $200 over $6400 = (200/6400)x100 = 3.125% for quarter

One year has 4 quarter therefore annual rate of interest = 3.125 x 4 = 12.5% P.A.

Answer Option E
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by unknown13 » Wed Jul 16, 2014 12:48 am
Hi
IMO the answer is E

thanks and regards

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by feedrom » Wed Jul 16, 2014 7:15 am
Good question, Abhasjha!