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tagged by: Max@Math Revolution

## Tom saved $10,000 at a constant compound interest rate of r ## Timer 00:00 ## Your Answer A B C D E ## Global Stats Difficult [Math Revolution GMAT math practice question] Tom saved$10,000 at a constant compound interest rate of r percent annually. After 10 years, the balance is double the principal. What will be the balance 30 years after the deposit?

A. $30,000 B.$40,000
C. $50,000 D.$60,000
E. $80,000 _________________ Math Revolution Finish GMAT Quant Section with 10 minutes to spare. The one-and-only Worldâ€™s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. Only$149 for 3 month Online Course
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Max@Math Revolution wrote:
[Math Revolution GMAT math practice question]

Tom saved $10,000 at a constant compound interest rate of r percent annually. After 10 years, the balance is double the principal. What will be the balance 30 years after the deposit? A.$30,000
B. $40,000 C.$50,000
D. $60,000 E.$80,000
Original deposit: 10,000.
The balance doubles every 10 years.
After 10 years, we get:
2*10,000 = 20,000.
After 20 years, we get:
2*20,000 = 40,000.
After 30 years, we get:
2*40,000 = 80,000.

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The question says,the balance got doubled in 10 years of time.This means Balance after 10 years is 10,000*2= 20,000$.Going by the same logic, and since in 20 years, the balance will be double of the balance in 10 years, which means 20,000*2= 40,000$. In another 10 years, that means, at the end of 30 years, the balance will again double up. The final balance will thus become 40,000*2= 80,000$. Hence Answer ### GMAT/MBA Expert Legendary Member Joined 24 Jul 2015 Posted: 2416 messages Followed by: 32 members Upvotes: 19 GMAT Score: => After 10 years, we have 10,000(1+r)^10 = 20,000 or (1+r)^10 = 2. So, after 30 years the balance is 10,000(1+r)^30 = 10,000((1+r)^10)^3= 10,000*2^3 =10,000*8 = 80,000. Therefore, the answer is E. Answer: E _________________ Math Revolution Finish GMAT Quant Section with 10 minutes to spare. The one-and-only Worldâ€™s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. Only$149 for 3 month Online Course
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