cangetgmat wrote:
I was stuck performing addition of GP.
+1 to you
You can do it using sum of GP as well.
\(2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8 = 1 + (1 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8)\)
The terms in brackets make a GP with first term = 1 and common ratio = 2
GP = \(1 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8\)
Sum of 9 terms of GP \(= 1(1 - 2^9)/(1-2) = 2^9 - 1\)
Sum of the required series = 1 + sum of GP = \(1 + 2^9 - 1 = 2^9\)
To check out a discussion on both the methods, check out my blog
http://www.veritasprep.com/blog/categor ... er-wisdom/ today evening. My this week's post discusses a question very similar to this one.
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Karishma
Veritas Prep GMAT Instructor
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