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27 May 2021, 08:45
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A
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
95%
(hard)
Question Stats:
29% (02:17) correct
71%
(02:29)
wrong
based on 68
sessions
History
Date
Time
Result
Not Attempted Yet
If \(x_n = a^{(2n-1)}\), where n is a positive integer then find sum of the first 10 terms \((x_1+x_2+----+x_{10})\)
1) \(x_1+x_2 = 10\)
2) \(a^2-a = 2\)
1) \(x_1+x_2 = 10\)
2) \(a^2-a = 2\)
Source: www.GMATinsight.com
27 May 2021, 14:46
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Ans should be A.
x1 = \(a\) ; x2 = \(a^3\) and so on. We need to find a in order to find the summation.
From (1)= \(a + a^3 \)= 10; \(a(1 + a^2)\)= 10 -----> \(a = 2\) --> We are sure that \( a\) is 2
From (2)= \(a^2-a-2\)=0 => a = -1,2 ---> We are not sure what the value of \(a\) is
x1 = \(a\) ; x2 = \(a^3\) and so on. We need to find a in order to find the summation.
From (1)= \(a + a^3 \)= 10; \(a(1 + a^2)\)= 10 -----> \(a = 2\) --> We are sure that \( a\) is 2
From (2)= \(a^2-a-2\)=0 => a = -1,2 ---> We are not sure what the value of \(a\) is
Archit3110
Major Poster
28 May 2021, 07:41
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for the given expression \(x_n = a^{(2n-1)}\)
x1 = a
x2 =a ^3
so on
target find sum of \((x_1+x_2+----+x_{10})\)
#1
\(x_1+x_2 = 10\)
a+a^3 = 10
possible when a = 2
sufficient
#2
\(a^2-a = 2\)
possible at a = 2 & -1
insufficient
option A
x1 = a
x2 =a ^3
so on
target find sum of \((x_1+x_2+----+x_{10})\)
#1
\(x_1+x_2 = 10\)
a+a^3 = 10
possible when a = 2
sufficient
#2
\(a^2-a = 2\)
possible at a = 2 & -1
insufficient
option A
GMATinsight
