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# powers

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Intern
Joined: 21 Apr 2010
Posts: 6
Followers: 0

Kudos [?]: 6 [0], given: 6

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26 Apr 2010, 03:16
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100% (00:00) correct 0% (00:00) wrong based on 1 sessions

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this is a question i got in my practise.. I will be writing ust the question and not the answer as i dont remember the answer and the options.

Please show how i can solve the question within 2 mins..

2+2+2+ 2^2 +2^3 +2^4+ 2^5 +2^6 +2^7+ 2^8+ 2^9
CEO
Status: Nothing comes easy: neither do I want.
Joined: 12 Oct 2009
Posts: 2795
Location: Malaysia
Concentration: Technology, Entrepreneurship
Schools: ISB '15 (M)
GMAT 1: 670 Q49 V31
GMAT 2: 710 Q50 V35
Followers: 220

Kudos [?]: 1513 [1] , given: 235

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26 Apr 2010, 03:31
1
KUDOS
ITC wrote:
this is a question i got in my practise.. I will be writing ust the question and not the answer as i dont remember the answer and the options.

Please show how i can solve the question within 2 mins..

2+2+2+ 2^2 +2^3 +2^4+ 2^5 +2^6 +2^7+ 2^8+ 2^9

$$2+2+2+ 2^2 +2^3 +2^4+ 2^5 +2^6 +2^7+ 2^8+ 2^9 = 4+2+ 2^2 +2^3 +2^4+ 2^5 +2^6 +2^7+ 2^8+ 2^9$$

now$$2+ 2^2 +2^3 +2^4+ 2^5 +2^6 +2^7+ 2^8+ 2^9 i$$s the sum of GP series with a =2 ,r=2 n = 9

sum of series is =$$\frac{a(r^n -1)}{(r-1)}= \frac{2* (2^9 -1)}{(2-1)}$$
= $$2^{10} - 2$$
so required sum is =$$2^{10} - 2 +4 = 2^{10} +2$$
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Joined: 05 Mar 2010
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26 Apr 2010, 03:51
This can be written as 2+(2^2+2^2+2^3+............+2^9)
2^2+2^2 = 2^3
2^3+2^3 = 2^4
so on ..............2^9+2^9 = 2^10

we will be left with 2+2^10 - answer
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Re: powers   [#permalink] 26 Apr 2010, 03:51
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