Mental Math: Years to Double an Investment

Sharing a very simple, but handy mental math rule that was mentioned in quite a few of our MBA classes, such as Investment Styles and Strategies, Designing Financial Models that Work and others:

If you want to quickly ballpark the # of years it will approximately take for an investment to double, then just divide 72 by the annual growth rate. For example, if your investment grows 7% a year, it will take slightly more than 10 years for it to double (72/7). But if it grows 36% a year, it will only take about two years to double (72/36). 

You can read more about this “Rule of 72” on Wikipedia. Now, you now you can come across as a math genius without much effort 😉

Math brainteasers from GMAT, 1

So, I also started preparing for this awesome GMAT exam. And now Saturday and Sunday mornings are devoted to studying which I haven’t been doing for years.So far, I try to learn concepts from Divisibility, Primes, Odds & Evens, Consecutive Integers and other amusing topics.

This is the first and test post in which I’d like to share few exercises that make me break some sweat. Let’s see if anybody is going to be interested. If yes, I might continue the series.

So, how about solving these 5 exercises?

 

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