total savings before investing

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total savings before investing

by sanju09 » Tue Apr 05, 2011 4:08 am
Shawn invested one half of his savings in a bond that paid simple interest for 2 years and received $550 as interest. He invested the remaining in a bond that paid compound interest, interest being compounded annually, for the same 2 years at the same rate of interest and received $605 as interest. What was the value of his total savings before investing in these two bonds?
(A) $2750
(B) $5500
(C) $11000
(D) $22000
(E) $44000
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by Anurag@Gurome » Tue Apr 05, 2011 4:32 am
sanju09 wrote:Shawn invested one half of his savings in a bond that paid simple interest for 2 years and received $550 as interest. He invested the remaining in a bond that paid compound interest, interest being compounded annually, for the same 2 years at the same rate of interest and received $605 as interest. What was the value of his total savings before investing in these two bonds?
(A) $2750
(B) $5500
(C) $11000
(D) $22000
(E) $44000
P*R*2/100 = 550 implies PR = 27500 or R = 27500/P
P + 605 = P[1 + R/100]²
P + 605 = P + PR²/10000 + PR/50
605 = P(27500)²/10000*P² + P*27500/50P
605 = 75625/P + 550 or 55 = 75625/P implies P = $1,375
Hence, total savings before investing in the two bonds = 2 * $1,375 = $2,750

The correct answer is A.
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by GMATGuruNY » Tue Apr 05, 2011 6:01 am
sanju09 wrote:Shawn invested one half of his savings in a bond that paid simple interest for 2 years and received $550 as interest. He invested the remaining in a bond that paid compound interest, interest being compounded annually, for the same 2 years at the same rate of interest and received $605 as interest. What was the value of his total savings before investing in these two bonds?
(A) $2750
(B) $5500
(C) $11000
(D) $22000
(E) $44000
We can plug in the answer choices.

When the $550 simple interest is converted to interest compounded annually, Shawn will receive 550/2 = $275 the first year and 605-275 = $330 the second year.
Thus, the correct answer choice must yield $330 as the second year interest.

Answer choice C: 11,000.
Half this amount = 11,000/2 = 5500.
Since 550 is 10% of 5500, the simple interest rate is 10%.
Compounded annually, Shawn will get 5% the first year, 5% the second year.
Amount at end of the first year = 5500 + 275 = 5775.
Interest second year = .05 * 5775 = 288.5.
Eliminate C.
We need a much higher compounded interest rate, so the initial amount must be much lower.

Answer choice A: 2750.
Half this amount = 2750/2 = 1375.
Since 10% of 1375 = 137.5, and 4*(137.5) = 550, the simple interest rate is 40%.
Compounded annually, Shawn will get 20% the first year, 20% the second year.
Amount at end of the first year = 1375 + 275 = 2650.
Interest second year = .2 * 2650 = 330. Success!

The correct answer is A.
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by mk101 » Wed Apr 06, 2011 10:25 am
sanju09 wrote:Shawn invested one half of his savings in a bond that paid simple interest for 2 years and received $550 as interest. He invested the remaining in a bond that paid compound interest, interest being compounded annually, for the same 2 years at the same rate of interest and received $605 as interest. What was the value of his total savings before investing in these two bonds?
(A) $2750
(B) $5500
(C) $11000
(D) $22000
(E) $44000

Another approach to this question -

SI For one year = 550 /2 = 275 = CI for the first year.

CI -SI ( the difference between CI and SI for two years = 605 -550 =55

CI for the firt year = SI for the first year

CI for the second year = SI for the 2nd year + SI on the SI accrued during the first year,

Thus the excess interest accrued = 605 -550 = 55

therefore 55 is the interest earned on Rs 275 during a span of one year.

r = 55/275 * 100 = 20 %

Thus at the rate of 20 % the principle = P * 20 * 1/ 100 = 275 thus P = Rs 1375

TOtal Principle = 2 * 1375 = Rs 2750