Word Problem

[sukhman]

A certain sum triples in 3 years under compound interest at a certain rate of interest. in how many years would the sum become 9 times itself at the same rate under compound interest.

[theCodeToGMAT]

3X = X (1+R/100)^3

9X = X(1+R/100)^T

9 = (1+R/100)^T

3 * 3 = (1+R/100)^T

(1+R/100)^3 * (1+R/100)^3 = (1+R/100)^T

T=6 years

What is the OA?

[Brent@GMATPrepNow]

A certain sum triples in 3 years under compound interest at a certain rate of interest. in how many years would the sum become 9 times itself at the same rate under compound interest.

Let's say that P = the original investment
If the amount triples every 3 years, we get:

Year 0: P dollars
Year 3: value = 3P dollars
Year 6: value = 9P dollars
Year 9: value = 27P dollars
Year 12: value = 81P dollars
Year 15: value = 243P dollars
etc.

So, we can see that, after 6 years, the value is 9 times the original investment.

Cheers,
Brent