InterviewSolution
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InterviewSolution
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find the value of x such that 1+4+7+10+….+x = 715 |
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Answer» Correct Answer - x=64 Here, a=1and d=3. Let it contain n terms. Then, ` n/2 .[ 3a+(n-1)d] = 715 Rightarrow n/2. [2xx 1 + ( n-1)xx3] = 715` ` Rightarrow n(3n-1) = 1430 Rightarrow 3n^(2)-n-1430 =0 Rightarrow 3n^(2)-66n+65n -1430=0` ` Rightarrow 3n(n-22) + 65 (n-22) =0Rightarrow (n-22) (3n+65) =0 Rightarrow n=22` `x==T_(22) = ( a+21d) = ( 1 + 21xx3) = 64` |
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